Plasma processing apparatus and method

ABSTRACT

An apparatus includes an upper electrode and a lower electrode for supporting a wafer disposed opposite each other within a process chamber. A first RF power supply configured to apply a first RF power having a relatively higher frequency is connected to the upper electrode. A second RF power supply configured to apply a second RF power having a relatively lower frequency is connected to the lower electrode. A variable DC power supply is connected to the upper electrode. A process gas is supplied into the process chamber while any one of application voltage, application current, and application power from the variable DC power supply to the upper electrode is controlled, to generate plasma of the process gas so as to perform plasma etching.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a continuation of application Ser. No.11/156,559, filed on Jun. 21, 2005, which claims the benefit of U.S.Provisional Applications No. 60/589,831, filed Jul. 22, 2004; No.60/650,957, filed Feb. 9, 2005; and No. 60/662,344, filed Mar. 17, 2005which are based upon and claims the benefit of priority from the priorJapanese Patent Applications No. 2004-183093, filed Jun. 21, 2004; No.2005-013912, filed Jan. 21, 2005; and No. 2005-045095, filed Feb. 22,2005, the entire contents of all of which are incorporated herein byreference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relate to a plasma processing apparatus, plasmaprocessing method, and computer readable storage medium, used forperforming a plasma process on a target substrate, such as asemiconductor substrate.

2. Description of the Related Art

For example, in manufacturing semiconductor devices, plasma etchingprocesses, which utilize plasma to etch a layer through a resist mask,are often used for forming a predetermined pattern on a predeterminedlayer disposed on a target substrate or semiconductor wafer.

There are various plasma etching apparatuses for performing such plasmaetching, but parallel-plate plasma processing apparatuses of thecapacitive coupling type are the ones in mainstream use.

In general, a parallel-plate plasma etching apparatus of the capacitivecoupling type includes a chamber with parallel-plate electrodes (upperand lower electrodes) disposed therein. While a process gas is suppliedinto the chamber, an RF (radio frequency) is applied to one of theelectrodes to form an electric field between the electrodes. The processgas is turned into plasma by the RF electric field, thereby performingplasma etching on a predetermined layer disposed on a semiconductorwafer.

More specifically, there is known a plasma etching apparatus in which anRF for plasma generation is applied to the upper electrode to generateplasma, while an RF for ion attraction is applied to the lower electrode(for example, Jpn. Pat. Appln. KOKAI Publication No. 2000-173993 (Patentpublication 1)). This plasma etching apparatus can form a suitableplasma state and realize an etching process with high selectivity andhigh reproducibility.

In recent years, owing to the demands of increased micro-fabrication,the thickness of photo-resist films used as masks is reduced, while thetype of photo-resist is shifted from KrF photo-resist (i.e., aphoto-resist to be exposed with a laser beam emitted from KrF gas) toArF photo-resist (i.e., a photo-resist to be exposed with ashorter-wavelength laser beam emitted from ArF gas), which allowsformation of pattern opening portions of about 0.13 μm or less.

However, since the ArF photo-resist has poor plasma resistanceproperties, its surface becomes rough during etching, which is scarcelycaused in the KrF resist. Accordingly, problems arise in that verticallines (striation) are formed on the inner wall of opening portions, oropening portions are expanded (increase in CD). These problems prevent,along with a small thickness of the photo-resist, etching holes frombeing formed with good etching selectivity.

On the other hand, in etching apparatuses of this kind, if the powerlevel of an RF power for plasma generation applied to the upperelectrode is too low, deposited substances (deposition) may remain onthe upper electrode after etching, thereby varying processcharacteristics or producing particles. By contrast, if the power levelis too high, the electrode may be etched, thereby bringing about processcharacteristics different from those obtained by a lower power level.The suitable range of power from the RF power supply depends on theprocess, and the process should not be fluctuated by the power. Further,in serial etching processes, deposition sticking to the chamber wallcauses a memory effect in that a previous process leaves some effectthat affects a subsequent process. Accordingly, it is preferable toreduce deposition on the chamber wall.

Furthermore, in parallel-plate etching apparatuses of the capacitivecoupling type, where the pressure in the chamber is high and the etchinggas in use is a negative gas (for example, CxFy or O₂), the plasmadensity becomes low at the chamber central portion, which makes itdifficult to control the plasma density.

On the other hand, owing to the demands of increased miniaturization andhigher speed through interconnection lines in semiconductor devices, useof inter-level insulating films having a low dielectric constantproceeds to reduce the parasitic capacitance of interconnection lines.Of the low dielectric constant films (Low-k films) of this kind, SiOCfamily films have attracted particularly attention.

Where plasma etching is performed on an organic Low-k film, such as anSiOC family film, it is important to ensure a sufficient selectivitybetween the organic Low-k film and a mask layer or an underlying filmof, e.g., silicon nitride. In general, a mixture gas based on afluorocarbon gas is used as a process gas to provide a relatively highselectivity relative to an underlying film, but it is insufficient asregards selectivity. For this reason, an etching method described belowhas been proposed in etching an SiOC family film to improve theselectivity relative to a silicon nitride film (for example, Jpn. Pat.Appln. KOKAI Publication No. 2002-270586 (Patent publication 2)).Specifically, plasma etching is performed on an SiOC family inter-levelinsulating film while a nitride film used as a barrier layer of a Cuinterconnection line is utilized as an underlying etching-stopper layer.In this method, C₄F₈/Ar/N₂ is used as a process gas with the flow-rateratio of Ar set to be 80% or more, thereby improving the selectivityrelative to the underlying film.

Further, similarly to Patent publication 2, an etching method describedbelow has been proposed (for example, Jpn. Pat. Appln. KOKAI PublicationNo. 2004-87875 (Patent publication 3)). Specifically, plasma etching isperformed on an SiOC family inter-level insulating film while a siliconnitride film is utilized as an underlying etching-stopper layer. Thismethod comprises a first etching step of using CHF₃/Ar/N₂ as a processgas and a second etching step of using C₄F₈/Ar/N₂ as a process gas,thereby improving the selectivity relative to both of the mask andsilicon nitride film.

However, as described above, silicon nitride used for a barrier layer ofa Cu interconnection line has good barrier properties, but has a highdielectric constant of 7.0. Accordingly, in order to sufficientlyutilize the low dielectric constant property of a Low-k film, such as anSiOC family film, a barrier layer having a still lower dielectricconstant is required, the representative of which is silicon carbide(SiC) having a dielectric constant of 3.5.

Where an SiC barrier layer having a low dielectric constant is used asan underlying etching-stopper layer, it is also necessary to ensure asufficient etching selectivity to etch a Low-k film or etching targetlayer disposed thereon. However, according to plasma etching using afluorocarbon family process gas, as described in Patent publication 2and Patent publication 3, it is difficult to ensure a sufficient etchingselectivity between the Low-k film and SiC layer.

BRIEF SUMMARY OF THE INVENTION

The present invention has been made in consideration of the problemsdescribed above, and has an object to provide a plasma processingapparatus and plasma processing method, which can realize highselectivity etching while maintaining the plasma resistance propertiesof a resist layer or organic mask layer at a high level, or caneffectively prevent deposition on an electrode, or can realize high rateetching, or can realize uniform etching on a target substrate.

Another object is to provide a plasma processing method which canrealize etching on a Low-k film with high etching selectivity relativeto an underlying SiC layer used as an etching-stopper layer.

According to a first aspect of the present invention, there is provideda plasma processing apparatus comprising: a process chamber configuredto accommodate a target substrate and to be vacuum-exhausted; a firstelectrode and a second electrode disposed opposite each other within theprocess chamber, the second electrode being configured to support thetarget substrate; a first RF power application unit configured to applya first RF power having a relatively higher frequency to the firstelectrode; a second RF power application unit configured to apply asecond RF power having a relatively lower frequency to the secondelectrode; a DC power supply configured to apply a DC voltage to thefirst electrode; a process gas supply unit configured to supply aprocess gas into the process chamber; and a control unit configured tocontrol any one of application voltage, application current, andapplication power from the DC power supply to the first electrode.

In this apparatus, it may be adopted that the DC power supply isconfigured such that any one of application voltage, applicationcurrent, and application power to the first electrode is variable. Inthis case, it may be adopted that the control unit is configured tocontrol whether the DC voltage is to be applied or not, from the DCpower supply to the first electrode. The apparatus may further comprisea detector configured to detect a generated plasma state, wherein thecontrol unit controls any one of application voltage, applicationcurrent, and application power from the DC power supply to the firstelectrode, based on information from the detector.

In the plasma processing apparatus according to the first aspect of thepresent invention, typically, the first electrode is an upper electrode,and the second electrode is a lower electrode. In this case, the firstRF power applied to the first electrode preferably has a frequency of13.56 MHz or more, and more preferably has a frequency of 40 MHz ormore. It is preferable that the second RF power applied to the secondelectrode has a frequency of 13.56 MHz or less.

In the plasma processing apparatus according to the first aspect of thepresent invention, it is preferable that the DC power supply isconfigured to apply a voltage within a range of −2,000 to +1,000V. It ispreferable that the DC voltage applied from the DC power supply has anabsolute value of 500V or more. It is preferable that the DC voltage isa negative voltage having an absolute value larger than that of aself-bias voltage generated on a surface of the first electrode by thefirst RF power applied to the first electrode. It may be adopted that asurface of the first electrode facing the second electrode is made of asilicon-containing substance.

In the plasma processing apparatus according to the first aspect of thepresent invention, it may be adopted that a conductive member regularlygrounded is disposed within the process chamber to release throughplasma a current caused by the DC voltage applied from the DC powersupply to the first electrode. In this case, it may be adopted that thefirst electrode is an upper electrode, the second electrode is a lowerelectrode, and the conductive member is disposed around the secondelectrode, or the conductive member is disposed near the firstelectrode. It may be adopted that the conductive member is disposed toform a ring shape around the first electrode. It may be adopted that thegrounded conductive member has a recess to prevent flying substancesfrom being deposited during a plasma process.

In the structure described above, it may be adopted that a cover plateis disposed to partly cover the conductive member, and the cover plateis moved relative to the conductive member by a driving mechanism tochange a portion of the conductive member to be exposed to plasma. Itmay be adopted that the conductive member is columnar and partly exposedto plasma, and the conductive member is rotated about a center thereofby a driving mechanism to change a portion of the conductive member tobe exposed to plasma. It may be adopted that a cover film having astepped shape and made of a material to be etched by plasma is disposedto partly cover the conductive member, and the cover film is configuredto be etched to change a portion of the conductive member to be exposedto plasma.

In the plasma processing apparatus according to the first aspect of thepresent invention, it may be adopted that a conductive member to begrounded based on a command from an overall control unit is disposedwithin the process chamber to release through plasma a current caused bythe DC voltage applied from the DC power supply to the first electrode.In this case, it may be adopted that the first electrode is an upperelectrode, the second electrode is a lower electrode, and the conductivemember is disposed around the second electrode, or the conductive memberis disposed near the first electrode. It may be adopted that theconductive member is disposed to form a ring shape around the firstelectrode. It may be adopted that the grounded conductive member has arecess to prevent flying substances from being deposited during a plasmaprocess. It may be adopted that the conductive member is grounded duringplasma etching.

It may be adopted that the conductive member is configured to besupplied with a DC voltage or AC voltage, and the DC voltage or ACvoltage is applied based on a command from an overall control unit tosputter or etch a surface thereof. In this case, it is preferable thatthe DC voltage or AC voltage is applied to the conductive member duringcleaning. The apparatus may further comprise a switching mechanismconfigured to switch connection of the conductive member between the DCpower supply and a ground line, wherein, when the conductive member isconnected to the DC power supply by the switching mechanism, the DCvoltage or AC voltage is applied from the DC power supply to theconductive member to sputter or etch a surface thereof. In thisstructure, it is preferable that the conductive member is configured tobe supplied with a negative DC voltage. Where a negative DC voltage isapplicable, it is preferable that a grounded conductive auxiliary memberis disposed within the process chamber to release a DC electron currentflowing thereinto when the negative DC voltage is applied to theconductive member. In this case, it may be adopted that the firstelectrode is an upper electrode, the second electrode is a lowerelectrode, the conductive member is disposed near the first electrode,and the conductive auxiliary member is disposed around the secondelectrode.

In the plasma processing apparatus according to the first aspect of thepresent invention, the apparatus may further comprise a conductivemember disposed within the process chamber and configured to take oneither one of a first state and a second state based on a command froman overall control unit, the first state being arranged to ground theconductive member to release through plasma a DC current applied fromthe DC power supply to the first electrode, and the second state beingarranged to apply a DC voltage from the DC power supply to theconductive member to sputter or etch a surface thereof; and a connectionswitching mechanism disposed to switch between first connection andsecond connection to form the first state and the second state,respectively, the first connection being arranged to connect a negativeterminal of the DC power supply to the first electrode and to connectthe conductive member to a ground line, and the second connection beingarranged to connect a positive terminal of the DC power supply to thefirst electrode and to connect the negative terminal of the DC powersupply to the conductive member. In this case, it is preferable that thefirst state is formed during plasma etching, and the second state isformed during cleaning of the conductive member.

According to a second aspect of the present invention, there is provideda plasma processing apparatus comprising: a process chamber configuredto accommodate a target substrate and to be vacuum-exhausted; a firstelectrode and a second electrode disposed opposite each other within theprocess chamber, the second electrode being configured to support thetarget substrate; a first RF power application unit configured to applya first RF power having a relatively higher frequency to the firstelectrode; a second RF power application unit configured to apply asecond RF power having a relatively lower frequency to the secondelectrode; a DC power supply configured to apply a DC voltage to thefirst electrode; a process gas supply unit configured to supply aprocess gas into the process chamber; and a control unit configured tocontrol any one of application voltage, application current, andapplication power from the DC power supply to the first electrode,wherein the first electrode includes an inner electrode and an outerelectrode, the first RF power is divided and applied to the innerelectrode and the outer electrode, and the DC power supply is connectedto at least one of the inner electrode and the outer electrode.

In the plasma processing apparatus according to the second aspect of thepresent invention, it may be adopted that the DC power supply isconfigured such that DC voltages applied to the inner electrode and theouter electrode are variable independently of each other. In this case,it may be adopted that the inner electrode and the outer electrode aresupplied with DC voltages from respective DC power supplies. It may beadopted that the power supply has one terminal connected to the innerelectrode, and another terminal connected to the outer electrode. Inthis case, it may be adopted that the DC power supply is configured suchthat any one of application voltage, application current, andapplication power is variable.

In this apparatus, it may be adopted that the control unit is configuredto control whether the DC voltage is to be applied or not, from the DCpower supply to the first electrode. The apparatus may further comprisea detector configured to detect a generated plasma state, wherein thecontrol unit controls any one of application voltage, applicationcurrent, and application power from the DC power supply to the firstelectrode, based on information from the detector.

In the plasma processing apparatus according to the second aspect of thepresent invention, typically, the first electrode is an upper electrode,and the second electrode is a lower electrode. In this case, the firstRF power applied to the first electrode preferably has a frequency of13.56 MHz or more, and more preferably has a frequency of 40 MHz ormore. It is preferable that the second RF power applied to the secondelectrode has a frequency of 13.56 MHz or less.

In the plasma processing apparatus according to the second aspect of thepresent invention, it may be adopted that the DC power supply isconfigured to apply a voltage within a range of −2,000 to +1,000V. It ispreferable that the DC voltage applied from the DC power supply has anabsolute value of 100V or more, and more preferably 500V or more. It ispreferable that the DC voltage is a negative voltage having an absolutevalue larger than that of a self-bias voltage generated on a surface ofthe first electrode by the first RF power applied to the firstelectrode. It may be adopted that a surface of the first electrodefacing the second electrode is made of a silicon-containing substance.

In the plasma processing apparatus according to the second aspect of thepresent invention, it may be adopted that a conductive member regularlygrounded is disposed within the process chamber to release throughplasma a current caused by the DC voltage applied from the DC powersupply to the first electrode. In this case, it may be adopted that thefirst electrode is an upper electrode, the second electrode is a lowerelectrode, and the conductive member is disposed around the secondelectrode, or the conductive member is disposed near the firstelectrode. It may be adopted that the grounded conductive member isdisposed to form a ring shape around the first electrode. It may beadopted that the conductive member has a recess to prevent flyingsubstances from being deposited during a plasma process.

In the structure described above, it may be adopted that a cover plateis disposed to partly cover the conductive member, and the cover plateis moved relative to the conductive member by a driving mechanism tochange a portion of the conductive member to be exposed to plasma. Itmay be adopted that the conductive member is columnar and partly exposedto plasma, and the conductive member is rotated about a center thereofby a driving mechanism to change a portion of the conductive member tobe exposed to plasma. It may be adopted that a cover film having astepped shape and made of a material to be etched by plasma is disposedto partly cover the conductive member, and the cover film is configuredto be etched to change a portion of the conductive member to be exposedto plasma.

In the plasma processing apparatus according to the second aspect of thepresent invention, it may be adopted that a conductive member to begrounded based on a command from an overall control unit is disposedwithin the process chamber to release through plasma a current caused bythe DC voltage applied from the DC power supply to the first electrode.In this case, it may be adopted that the first electrode is an upperelectrode, the second electrode is a lower electrode, and the conductivemember is disposed around the second electrode, or the conductive memberis disposed near the first electrode. It may be adopted that theconductive member is disposed to form a ring shape around the firstelectrode. It may be adopted that the conductive member has a recess toprevent flying substances from being deposited during a plasma process.It may be adopted that the conductive member is grounded during plasmaetching.

It may be adopted that the conductive member is configured to besupplied with a DC voltage or AC voltage, and the DC voltage or ACvoltage is applied based on a command from an overall control unit tosputter or etch a surface of the conductive member. In this case, it ispreferable that the DC voltage or AC voltage is applied to theconductive member during cleaning. The apparatus may further comprise aswitching mechanism configured to switch connection of the conductivemember between the DC power supply and a ground line, wherein, when theconductive member is connected to the DC power supply by the switchingmechanism, the DC voltage or AC voltage is applied from the DC powersupply to the conductive member to sputter or etch a surface thereof. Inthis structure, it is preferable that the conductive member isconfigured to be supplied with a negative DC voltage. Where a negativeDC voltage is applicable, it is preferable that a grounded conductiveauxiliary member is disposed within the process chamber to release a DCelectron current flowing thereinto when the negative DC voltage isapplied to the conductive member. In this case, it may be adopted thatthe first electrode is an upper electrode, the second electrode is alower electrode, the conductive member is disposed near the firstelectrode, and the conductive auxiliary member is disposed around thesecond electrode.

In the plasma processing apparatus according to the second aspect of thepresent invention, the apparatus may further comprise a conductivemember disposed within the process chamber and configured to take oneither one of a first state and a second state based on a command froman overall control unit, the first state being arranged to ground theconductive member to release through plasma a DC current applied fromthe DC power supply to the first electrode, and the second state beingarranged to apply a DC voltage from the DC power supply to theconductive member to sputter or etch a surface thereof; and a connectionswitching mechanism disposed to switch between first connection andsecond connection to form the first state and the second state,respectively, the first connection being arranged to connect a negativeterminal of the DC power supply to the first electrode and to connectthe conductive member to a ground line, and the second connection beingarranged to connect a positive terminal of the DC power supply to thefirst electrode and to connect the negative terminal of the DC powersupply to the conductive member. In this case, it is preferable that thefirst state is formed during plasma etching, and the second state isformed during cleaning of the conductive member.

According to a third aspect of the present invention, there is provideda plasma processing method using a process chamber with a firstelectrode and a second electrode disposed opposite each other therein,the second electrode being configured to support a target substrate, themethod comprising supplying a process gas into the process chamber,while applying a first RF power having a relatively higher frequency tothe first electrode, and applying a second RF power having a relativelylower frequency to the second electrode, to generate plasma of theprocess gas, thereby performing a plasma process on a target substratesupported by the second electrode, wherein the method comprises:applying a DC voltage to the first electrode; and performing the plasmaprocess on the target substrate while the applying the DC voltage to thefirst electrode.

In the plasma processing method according to the third aspect of thepresent invention, typically, the first electrode is an upper electrode,and the second electrode is a lower electrode. In this case, it ispreferable that the DC voltage is a negative voltage having an absolutevalue larger than that of a self-bias voltage generated on a surface ofthe first electrode by the first RF power applied to the firstelectrode. It is preferable that the first RF power applied to the upperelectrode has a frequency of 13.56 to 60 MHz, and the second RF powerapplied to the lower electrode has a frequency of 300 kHz to 13.56 MHz.It is preferable that the process gas is a gas containing fluorocarbon.In this case, it is preferable that the gas containing fluorocarboncontains at least C₄F₈. It may be adopted that the gas containingfluorocarbon further contains an inactive gas. It may be adopted thatthe insulating film is an organic insulating film. In this case, it maybe adopted that the organic insulating film is an SiOC family film. Inthis case, it is preferable that an underlying film made of siliconcarbide (SiC) is disposed under the SiOC family film.

In the plasma processing method according to the third aspect of thepresent invention, it is preferable that the DC voltage has an absolutevalue of 1,500V or less. It is preferable that a process pressure is setat 1.3 to 26.7 Pa (10 to 200 mTorr). It is preferable that the first RFpower applied to the first electrode is set at 3,000 W or less. It ispreferable that the second RF power applied to the second electrode isset at 100 to 5,000 W. It is preferable that the process gas is amixture gas of C₄F₈, N₂, and Ar, with a flow-rate ratio of C₄F₈/N₂/Ar=[4to 20]/[100 to 500]/[500 to 1,500] mL/min (sccm). The plasma processingmethod described above may be applied to an over etching step.

In the plasma processing method according to the third aspect of thepresent invention, it may be adopted that the method comprises etchingan insulating film on the target substrate supported by the secondelectrode, wherein the process gas comprises a combination of C₅F₈, Ar,and N₂ to increase selectivity of the insulating film relative to anunderlying film. It may be adopted that the method comprises etching aninsulating film on the target substrate supported by the secondelectrode, wherein the process gas comprises CF₄ or a combination ofC₄F₈, CF₄, Ar, N₂, and O₂ to increase selectivity of the insulating filmrelative to a mask. It may be adopted that the method comprises etchingan insulating film on the target substrate supported by the secondelectrode, wherein the process gas comprises any one of a combination ofC₄F₆, CF₄, Ar, and O₂, a combination of C₄F₆, C₃F₈, Ar, and O₂, and acombination of C₄F₆, CH₂F₂, Ar, and O₂ to increase an etching rate ofthe insulating film.

According to a fourth aspect of the present invention, there is provideda plasma processing method using a process chamber with a firstelectrode and a second electrode disposed opposite each other therein,the first electrode including an inner electrode and an outer electrode,and the second electrode being configured to support a target substrate,the method comprising supplying a process gas into the process chamber,while applying a first RF power having a relatively higher frequency tothe first electrode, and applying a second RF power having a relativelylower frequency to the second electrode, to generate plasma of theprocess gas, thereby performing a plasma process on a target substratesupported by the second electrode, wherein the method comprises:applying a DC voltage to at least one of the inner electrode and theouter electrode; and performing the plasma process on the targetsubstrate while the applying the DC voltage to the first electrode.

In the plasma processing method according to the fourth aspect of thepresent invention, it may be adopted that the method comprises etchingan insulating film on the target substrate supported by the secondelectrode, wherein the process gas comprises a combination of C₅F₈, Ar,and N₂ to increase selectivity of the insulating film relative to anunderlying film. It may be adopted that the method comprises etching aninsulating film on the target substrate supported by the secondelectrode, wherein the process gas comprises CF₄ or a combination ofC₄F₈, CF₄, Ar, N₂, and O₂ to increase selectivity of the insulating filmrelative to a mask. It may be adopted that the method comprises etchingan insulating film on the target substrate supported by the secondelectrode, wherein the process gas comprises any one of a combination ofC₄F₆, CF₄, Ar, and O₂, a combination of C₄F₆, C₃F₈, Ar, and O₂, and acombination of C₄F₆, CH₂F₂, Ar, and O₂ to increase an etching rate ofthe insulating film.

According to a fifth aspect of the present invention, there is provideda computer storage medium storing a control program for execution on acomputer, wherein the control program, when executed, controls a plasmaprocessing apparatus to perform the plasma processing method accordingto the third aspect.

According to a sixth aspect of the present invention, there is provideda computer storage medium storing a control program for execution on acomputer, wherein the control program, when executed, controls a plasmaprocessing apparatus to perform the plasma processing method accordingto the fourth aspect.

According to the first aspect of the present invention, the first RFpower application unit configured to apply a first RF power having arelatively higher frequency is connected to the first electrode, thesecond RF power application unit configured to apply a second RF powerhaving a relatively lower frequency is connected to the second electrodefor supporting a target substrate, and the DC power supply configured toapply a DC voltage is connected to the first electrode. With thisarrangement, when the first RF power for generating plasma of a processgas, and the second RF power for attracting ions onto the targetsubstrate are applied to perform a plasma process, the DC voltage isfurther applied to the first electrode. As a consequence, it is possibleto exercise at least one of (1) the effect of increasing the absolutevalue of a self-bias voltage to the first electrode to sputter the firstelectrode surface, (2) the effect of expanding the plasma sheath on thefirst electrode side to press the plasma, (3) the effect of irradiatingthe target substrate with electrons generated near the first electrode,(4) the effect of controlling the plasma potential, (5) the effect ofincreasing the electron (plasma) density, and (6) the effect ofincreasing the plasma density at the central portion.

With the effect (1) described above, even if polymers derived from aprocess gas and a photo-resist are deposited on the surface of the firstelectrode, the polymers are sputtered, thereby cleaning up the surfaceof the first electrode. Further, an optimum quantity of polymers can besupplied onto the substrate, thereby canceling the surface roughness ofthe photo-resist film. Further, since the body of the electrode issputtered, the electrode material can be supplied onto the substrate,thereby reinforcing an organic mask made of, e.g., a photo-resist film.

With the effect (2) described above, the effective residence time abovethe target substrate is decreased, and the plasma concentrates above thetarget substrate with less diffusion, thereby reducing the dissociationspace. In this case, dissociation of a fluorocarbon family process gasis suppressed for an organic mask made of, e.g., a photo-resist film tobe less etched.

With the effect (3) described above, the composition of a mask on thetarget substrate is reformed and the roughness of the photo-resist filmis cancelled. Further, since the target substrate is irradiated withelectrons at a high velocity, the shading effect is suppressed andmicro-fabrication is thereby improved on the target substrate.

With the effect (4) described above, the plasma potential can besuitably controlled to prevent etching by-products from being depositedon members inside the process chamber, such as the electrodes, chamberwall (e.g., deposition shield), and insulating members.

With the effect (5) described above, the etching rate (etching speed) onthe target substrate is improved.

With the effect (6) described above, even where the pressure inside theprocess chamber is high and the etching gas employed is a negative gas,the plasma density is prevented from being lower at the central portionthan at the peripheral portion within the process chamber (suppressinggeneration of negative ions), so as to control the plasma density to bemore uniform.

As a consequence, the plasma resistance property of an organic masklayer made of, e.g., a resist layer remains high, so that the etchingcan be performed with high selectivity. Alternatively, the electrodescan be effectively free from deposited substances. Alternatively, theetching can be performed on the target substrate at a high rate oruniformly.

According to the second aspect of the present invention, the firstelectrode is divided into the inner electrode and outer electrode, thefirst RF power is divided and applied to the inner electrode and outerelectrode, and the DC power supply is connected to at least one of them.As a consequence, in addition to the effects described above, theelectric field intensities on the inner electrode and outer electrodesides can be changed, so that the plasma density uniformity is improved.

According to the third to sixth aspects of the present invention, afirst RF power and a DC voltage are applied to the first electrode toperform etching. As a consequence, it is possible to obtain a sufficientselectivity of an insulating film or etching target layer relative to anunderlying film. For example, where the insulating film is an SiOCfamily film, which is an organic insulating film, and the underlyingfilm is made of silicon carbide, or where the insulating film is an SiO₂film, which is an inorganic insulating film, and the underlying film ismade of silicon nitride, it is possible to perform etching whilesuppressing the underlying film being etched, as far as possible.

Further, by controlling etching conditions, such as RF power, pressure,and gas type, while applying a DC voltage to the first electrode, theetching rate of the SiOC family film or the like can be improved withhigh selectivity being maintained, as described above. In addition, theetching selectivity of the SiOC family film or the like relative toresist, particularly ArF resist, can be further improved. Further, sinceincrease in the etching rate and control of the etching pattern CD(Critical Dimension) can be attained together, it is possible to realizeetching with a high rate and accuracy, as well as improving reliabilityof the semiconductor device. Furthermore, where etching is performed toform a line-and-space pattern on a target substrate, such as asemiconductor wafer, the line etching roughness (LER) can be reduced.

Additional objects and advantages of the invention will be set forth inthe description which follows, and in part will be obvious from thedescription, or may be learned by practice of the invention. The objectsand advantages of the invention may be realized and obtained by means ofthe instrumentalities and combinations particularly pointed outhereinafter.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

The accompanying drawings, which are incorporated in and constitute apart of the specification, illustrate presently preferred embodiments ofthe invention, and together with the general description given above andthe detailed description of the preferred embodiments given below, serveto explain the principles of the invention.

FIG. 1 is a sectional view schematically showing a plasma etchingapparatus according to an embodiment 1 of the present invention;

FIG. 2 is a view showing a matching unit connected to a first RF powersupply in the plasma etching apparatus shown in FIG. 1;

FIG. 3 is a view showing change in V_(dc) and plasma sheath length wherea DC voltage is applied to the upper electrode in the plasma etchingapparatus shown in FIG. 1;

FIGS. 4A and 4B are views showing plasma states where a DC voltage isapplied to the upper electrode and where no DC voltage is applied to theupper electrode, respectively, in the plasma etching apparatus shown inFIG. 1;

FIG. 5 is a graph showing an etching rate for a photo-resist film, anetching rate for an SiO₂ film, and selectivity of the SiO₂ film relativeto the photo-resist film, where etching is performed on the SiO₂ filmwhile the DC voltage applied to the upper electrode is set at differentvalues in the plasma etching apparatus shown in FIG. 1;

FIG. 6 is a view showing a multi-layer film to which serial etchingprocesses are applied;

FIG. 7 is a view showing change in plasma potential waveforms where a DCvoltage is applied to the upper electrode in the plasma etchingapparatus shown in FIG. 1;

FIG. 8 is a view showing the relationship between the DC voltage appliedto the upper electrode and the maximum value of the plasma potential inthe plasma etching apparatus shown in FIG. 1;

FIG. 9 is a view showing change in electron density and distributionthereof where the DC voltage applied is set at different values in theplasma etching apparatus shown in FIG. 1;

FIGS. 10A to 10C are views schematically showing etched states at thecenter and edge obtained by respective values of the DC voltage used inthe etching of FIG. 9;

FIG. 11 is a view showing the relationship between the self-bias voltageon the upper electrode surface and the DC voltage applied;

FIG. 12 is a sectional view showing a modification of the plasma etchingapparatus shown in FIG. 1, provided with a detector for detectingplasma;

FIG. 13 is a view showing a waveform for suppressing abnormal electricdischarge where a DC voltage is applied to the upper electrode in theplasma etching apparatus shown in FIG. 1;

FIG. 14 is a schematic view showing another layout of a GND block;

FIG. 15 is a schematic view showing another layout of the GND block;

FIGS. 16A and 16B are views showing structures for preventing depositionon the GND block;

FIG. 17 is a schematic view showing an example of a device that canremove deposition on the GND block;

FIGS. 18A and 18B are schematic views showing a state in plasma etchingand a state in cleaning, respectively, of the device shown in FIG. 1;

FIG. 19 is a schematic view showing another state in plasma etching ofthe device shown in FIG. 17;

FIG. 20 is a schematic view showing another example of a device that canremove deposition on the GND block;

FIGS. 21A and 21B are schematic views showing a state in plasma etchingand a state in cleaning, respectively, of the device shown in FIG. 20;

FIG. 22 is a schematic view showing an example of the GND block having afunction to prevent it from losing the grounding performance in thesense of DC;

FIG. 23 is a schematic view showing another example of the GND blockhaving a function to prevent it from losing the grounding performance inthe sense of DC;

FIGS. 24A and 24B are schematic views each showing another example ofthe GND block having a function to prevent it from losing the groundingperformance in the sense of DC;

FIG. 25 is a schematic view showing another example of the GND blockhaving a function to prevent it from losing the grounding performance inthe sense of DC;

FIG. 26 is a schematic view showing another example of the GND blockhaving a function to prevent it from losing the grounding performance inthe sense of DC;

FIG. 27 is a schematic view showing another example of the GND blockhaving a function to prevent it from losing the grounding performance inthe sense of DC;

FIG. 28 is a view showing the electron temperature distribution of RFplasma and DC plasma;

FIG. 29 is a view showing an electron temperature distribution of plasmaobtained by solely using an RF power, in comparison with that obtainedby applying a DC voltage along with an RF power;

FIGS. 30A and 30B are views for explaining following ability of ionswhere the bias RF power has a frequency of 2 MHz and a frequency of13.56 MHz, respectively;

FIG. 31 is a view showing ion energy distributions where the bias RFpower has a frequency of 2 MHz and a frequency of 13.56 MHz;

FIGS. 32A and 32B are schematic views showing an example of a wafersectional structure, which can be etched by the plasma etching apparatusshown in FIG. 1;

FIGS. 33A and 33B are schematic views showing another example of a wafersectional structure, which can be etched by the plasma etching apparatusshown in FIG. 1;

FIG. 34 is a sectional view schematically showing a plasma etchingapparatus according to an embodiment 2 of the present invention;

FIG. 35 is a sectional view schematically showing a main portion of theplasma etching apparatus shown in FIG. 34;

FIG. 36 is a circuit diagram showing an equivalent circuit of a mainportion of plasma generating means in the plasma etching apparatus shownin FIG. 34;

FIG. 37 is a view showing the relationship between the capacitance valueof a variable capacitor and electric field intensity ratio in the plasmaetching apparatus shown in FIG. 34;

FIG. 38 is a view showing a modification of the arrangement to apply aDC voltage to the upper electrode in the plasma etching apparatus shownin FIG. 34; and

FIG. 39 is a view showing another modification of the arrangement toapply a DC voltage to the upper electrode in the plasma etchingapparatus shown in FIG. 34.

DETAILED DESCRIPTION OF THE INVENTION

Embodiments of the present invention will be described hereinafter withreference to the accompanying drawings.

An embodiment 1 will be explained first. FIG. 1 is a sectional viewschematically showing a plasma etching apparatus according to theembodiment 1 of the present invention.

This plasma etching apparatus is structured as a parallel-plate plasmaetching apparatus of the capacitive coupling type. The apparatusincludes a cylindrical chamber (process chamber) 10, which is made of,e.g., aluminum with an anodization-processed surface. The chamber 10 isprotectively grounded.

A columnar susceptor pedestal 14 is disposed on the bottom of thechamber 10 through an insulating plate 12 made of, e.g., a ceramic. Asusceptor 16 made of, e.g., aluminum is disposed on the susceptorpedestal 14. The susceptor 16 is used as a lower electrode, on which atarget substrate, such as a semiconductor wafer W, is placed.

The susceptor 16 is provided with an electrostatic chuck 18 on the top,for holding the semiconductor wafer W by an electrostatic attractionforce. The electrostatic chuck 18 comprises an electrode 20 made of aconductive film, and a pair of insulating layers or insulating sheetssandwiching the electrode 20. The electrode 20 is electrically connectedto a direct current (DC) power supply 22. The semiconductor wafer W isattracted and held on the electrostatic chuck 18 by an electrostaticattraction force, e.g., a Coulomb force, generated by a DC voltageapplied from the DC power supply 22.

A conductive focus ring (correction ring) 24 made of, e.g., silicon isdisposed on the top of the susceptor 16 to surround the electrostaticchuck 18 (and the semiconductor wafer W) to improve etching uniformity.A cylindrical inner wall member 26 made of, e.g., quartz is attached tothe side of the susceptor 16 and susceptor pedestal 14.

The susceptor pedestal 14 is provided with a cooling medium space 28formed therein and annularly extending therethrough. A cooling mediumset at a predetermined temperature, such as cooling water, is circulatedwithin the cooling medium space 28 from a chiller unit (not shown)through lines 30 a and 30 b. The temperature of the cooling medium isset to control the process temperature of the semiconductor wafer Wplaced on the susceptor 16.

Further, a heat transmission gas, such as He gas, is supplied from aheat transmission gas supply unit (not shown), through a gas supply line32, into the interstice between the top surface of the electrostaticchuck 18 and the bottom surface of the semiconductor wafer W.

An upper electrode 34 is disposed above the lower electrode or susceptor16 in parallel with the susceptor. The space between the electrodes 16and 34 is used as a plasma generation space. The upper electrode 34defines a surface facing the semiconductor wafer W placed on the lowerelectrode or susceptor 16, and thus this facing surface is in contactwith the plasma generation space.

The upper electrode 34 is supported at the top of the chamber 10 by aninsulating shield member 42. The upper electrode 34 includes anelectrode plate 36 defining the facing surface opposite the susceptor 16and having a number of gas delivery holes 37, and an electrode support38 detachably supporting the electrode plate 36. The electrode support38 is made of a conductive material, such as aluminum with ananodization-processed surface, and has a water-cooling structure. Theelectrode plate 36 is preferably made of a conductor or semiconductorhaving a low resistivity and thus generating less Joule heat. Further,in order to reinforce a resist film, as described later, the electrodeplate 36 is preferably made of a silicon-containing substance. In lightof these factors, the electrode plate 36 is preferably made of siliconor SiC. The electrode support 38 has a gas diffusion cell 40 formedtherein, which is connected to the gas delivery holes 37 through anumber of gas flow channels 41 extending downward.

Further, the electrode support 38 has a gas feed port 62 formed thereinfor feeding a process gas into the gas diffusion cell 40. The gas feedport 62 is connected to a process gas supply source 66 through a gassupply line 64. The gas supply line 64 is provided with a mass-flowcontroller (MFC) 68 and a switching valve 70 disposed thereon in thisorder from the upstream (an FCN may be used in place of the MFC). Aprocess gas for etching, such as a fluorocarbon gas (CxFy), e.g., C₄F₈gas, is supplied from the process gas supply source 66 through the gassupply line 64 into the gas diffusion cell 40. Then, the process gasflows through the gas flow channels 41 and is delivered from the gasdelivery holes 37 into the plasma generation space, as in a showerdevice. Accordingly, in other words, the upper electrode 34 functions asa showerhead for supplying a process gas.

The upper electrode 34 is electrically connected to a first RF powersupply 48 through a matching unit 46 and a feed rod 44. The first RFpower supply 48 outputs an RF power with a frequency of 13.56 MHz ormore, such as 60 MHz. The matching unit 46 is arranged to match the loadimpedance with the internal (or output) impedance of the first RF powersupply 48. When plasma is generated within the chamber 10, the matchingunit 44 performs control for the load impedance and the output impedanceof the first RF power supply 48 to apparently agree with each other. Theoutput terminal of the matching unit 46 is connected to the top of thefeed rod 44.

Further, the upper electrode 34 is electrically connected to a variableDC power supply 50 in addition to the first RF power supply 48. Thevariable DC power supply 50 may be formed of a bipolar power supply.Specifically, the variable DC power supply 50 is connected to the upperelectrode 34 through the matching unit 46 and feed rod 44, and theelectric feeding can be set on/off by an on/off switch 52. The polarity,current, and voltage of the variable DC power supply 50, and the on/offswitch 52 are controlled by a controller (control unit) 51.

As shown in FIG. 2, the matching unit 46 includes a first variablecapacitor 54 branched from a feed line 49 of the first RF power supply48, and a second variable capacitor 56 disposed on the feed line 49downstream from the branch point, so as to exercise the functiondescribed above. The matching unit 46 also includes a filter 58configured to trap the RF (for example, 60 MHz) from the first RF powersupply 48 and the RF (for example, 2 MHz) from a second RF power supplydescribed later, so that a DC voltage current (which will be simplyreferred to as a DC voltage) is effectively supplied to the upperelectrode 34. As a consequence, a DC current is connected from thevariable DC power supply 50 through the filter 58 to the feed line 49.The filter 58 is formed of a coil 59 and a capacitor 60 arranged to trapthe RF from the first RF power supply 48 and the RF from the second RFpower supply described later.

The sidewall of the chamber 10 extends upward above the height level ofthe upper electrode 34 and forms a cylindrical grounded conductive body10 a. The top wall of the cylindrical grounded conductive body 10 a iselectrically insulated from the upper feed rod 44 by a tube-likeinsulating member 44 a.

The susceptor 16 used as a lower electrode is electrically connected toa second RF power supply 90 through a matching unit 88. The RF powersupplied from the second RF power supply 90 to the lower electrode orsusceptor 16 is used for attracting ions toward the semiconductor waferW. The second RF power supply 90 outputs an RF power with a frequency of300 kHz to 13.56 MHz, such as 2 MHz. The matching unit 88 is arranged tomatch the load impedance with the internal (or output) impedance of thesecond RF power supply 90. When plasma is generated within the chamber10, the matching unit 88 performs control for the load impedance and theinternal impedance of the second RF power supply 90 to apparently agreewith each other.

The upper electrode 34 is electrically connected to a low-pass filter(LPF) 92, which prevents the RF (60 MHz) from the first RF power supply48 from passing through, while it allows the RF (2 MHz) from the secondRF power supply 98 to pass through to ground. The low-pass filter (LPF)92 is preferably formed of an LR filter or LC filter. On the other hand,the lower electrode or susceptor 16 is electrically connected to ahigh-pass filter (HPF) 94, which allows the RF (60 MHz) from the firstRF power supply 48 to pass through to ground.

An exhaust port 80 is formed at the bottom of the chamber 10, and isconnected to an exhaust unit 84 through an exhaust line 82. The exhaustunit 84 includes a vacuum pump, such as a turbo molecular pump, toreduce the pressure inside the chamber 10 to a predetermined vacuumlevel. A transfer port 85 for a semiconductor wafer W is formed in thesidewall of the chamber 10, and is opened/closed by a gate valve 86attached thereon. A deposition shield 11 is detachably disposed alongthe inner wall of the chamber 10 to prevent etching by-products(deposition) from being deposited on the wall. In other words, thedeposition shield 11 constitutes a chamber wall. A deposition shield 11is also disposed around the inner wall member 26. An exhaust plate 83 isdisposed at the bottom of the chamber 10 between the deposition shield11 on the chamber wall and the deposition shield 11 on the inner wallmember 26. The deposition shield 11 and exhaust plate 83 are preferablymade of an aluminum body covered with a ceramic, such as Y₂O₃.

A conductive member (GND block) 91 is disposed on a portion of thedeposition shield 11 that constitutes the chamber inner wall, at aheight essentially the same as the wafer W, and is connected to groundin the sense of DC. This arrangement provides the effect of preventingabnormal electric discharge, as described later.

Respective portions of the plasma etching apparatus are connected to andcontrolled by a control section (overall control unit) 95. The controlsection 95 is connected to a user interface 96 including, e.g., akeyboard and a display, wherein the keyboard is used for a processoperator to input commands for operating the plasma etching apparatus,and the display is used for showing visualized images of the operationalstatus of the plasma processing apparatus.

Further, the control section 95 is connected to a storage section 97that stores control programs for the control section 95 to control theplasma etching apparatus so as to perform various processes, andprograms or recipes for respective components of the plasma etchingapparatus to perform processes in accordance with process conditions.Recipes may be stored in a hard disk or semiconductor memory, or storedin a computer readable portable storage medium, such as a CDROM or DVD,to be attached to a predetermined position in the storage section 97.

A required recipe is retrieved from the storage section 97 and executedby the control section 95 in accordance with an instruction or the likethrough the user interface 96. As a consequence, the plasma etchingapparatus can perform a predetermined process under the control of thecontrol section 95. It should be noted that each of the plasmaprocessing apparatuses (plasma etching apparatuses) according toembodiments of the present invention includes such a control section 95.

When an etching process is performed in the plasma etching apparatusdescribed above, the gate valve 86 is first opened, and a semiconductorwafer W to be etched is transferred into the chamber 10 and placed onthe susceptor 16. Then, a process gas for etching is supplied from theprocess gas supply source 66 into the gas diffusion cell 40 at apredetermined flow rate, and then supplied into the chamber 10 throughthe gas flow channels 41 and gas delivery holes 37. At the same time,the interior of the chamber 10 is exhausted by the exhaust unit 84 toset the pressure inside the chamber 10 to be a predetermined valuewithin a range of, e.g., 0.1 to 150 Pa. The process gas may be selectedfrom various gases conventionally employed, and preferably is a gascontaining a halogen element, a representative of which is afluorocarbon gas (CxFy), such as C₄F₈ gas. Further, the process gas maycontain another gas, such as Ar gas or O₂ gas.

While the etching gas is supplied into the chamber 10, an RF power forplasma generation is applied from the first RF power supply 48 to theupper electrode 34 at a predetermined power level. At the same time, anRF for ion attraction is applied from the second RF power supply 90 tothe lower electrode or susceptor 16 at a predetermined power level.Also, a predetermined DC voltage is applied from the variable DC powersupply 50 to upper electrode 34. Further, a DC voltage is applied fromthe DC power supply 22 to the electrode 20 of the electrostatic chuck 18to fix the semiconductor wafer W on the susceptor 16.

The process gas delivered from the gas delivery holes 37 formed in theelectrode plate 36 of the upper electrode 34 is turned into plasma byglow discharge caused by the RF power applied across the upper electrode34 and the lower electrode or susceptor 16. Radicals and ions generatedin this plasma are used to etch the target surface of the semiconductorwafer W.

As described above, a first RF power for plasma generation is applied tothe upper electrode 34 to adjust the plasma density. At the same time, asecond RF power for ion attraction is applied to the lower electrode orsusceptor 16 to adjust the voltage. As a consequence, the plasma controlmargin can be set broader.

In this embodiment, when plasma is generated, the upper electrode 34 issupplied with an RF power within a range covering high frequencies (forexample, 10 MHz or more). As a consequence, the plasma density isincreased with a preferable state, so that high density plasma isgenerated even under a low pressure condition.

When the plasma is thus generated, a DC voltage with a predeterminedpolarity and value is applied from the variable DC power supply 50 tothe upper electrode 34. At this time, the application electrode or upperelectrode 34 is preferably set to have a self bias voltage V_(dc) on thesurface, at a level for obtaining a predetermined (moderate) sputteringeffect onto the surface, i.e., the surface of the electrode plate 36. Inother words, the application voltage from the variable DC power supply50 is preferably controlled by the controller 51 to increase theabsolute value of V_(dc) on the surface of the upper electrode 34. Wherethe RF power applied from the first RF power supply 48 is low, polymersare deposited on the upper electrode 34. However, since a suitable DCvoltage is applied from the variable DC power supply 50, polymersdeposited on the upper electrode 34 are sputtered, thereby cleaning upthe surface of the upper electrode 34. Further, an optimum quantity ofpolymers can be supplied onto the semiconductor wafer W, therebycanceling the surface roughness of the photo-resist film. Where thevoltage applied from the variable DC power supply 50 is adjusted tosputter the body of the upper electrode 34, the electrode material canbe supplied onto the surface of the semiconductor wafer W. In this case,the photo-resist film is provided with carbide formed on the surface,and is thereby reinforced. Further, the sputtered electrode materialreacts with F contained in a fluorocarbon family process gas and isexhausted, thereby reducing the F ratio in plasma for the photo-resistfilm to be less etched. Particularly, where the electrode plate 36 ismade of a silicon-containing material, such as silicon or SiC, sputteredsilicon from the surface of the electrode plate 36 reacts with polymers,so the photo-resist film is provided with SiC formed on the surface, andis thereby remarkably reinforced. In addition to this, Si is highlyreactive with F, and the effects described above are enhanced.Accordingly, a silicon-containing material is preferably used as amaterial of the electrode plate 36. It should be noted that, in thiscase, the application current or application power may be controlled inplace of the application voltage from the variable DC power supply 50.

The DC voltage thus applied to the upper electrode 34 to make a deepself bias voltage V_(dc), as described above, increases the length of aplasma sheath formed on the upper electrode 34, as shown in FIG. 3. Asthe length of the plasma sheath is increased, the plasma is furtherpressed by that much. For example, where no DC voltage is applied to theupper electrode 34, V_(dc) on the upper electrode side becomes, e.g.,−300V. In this case, the plasma sheath has a small length d₀, as shownin FIG. 4A. On the other hand, where a DC voltage of −900V is applied tothe upper electrode 34, V_(dc) on the upper electrode side becomes−900V. In this case, since the length of the plasma sheath is inproportion to ¾ of the absolute value of V_(dc), the plasma sheath has alarger length d_(l), and the plasma is pressed by that much, as shown inFIG. 4B. Where the length of the plasma sheath is thus increased tosuitably press the plasma, the effective residence time above thesemiconductor wafer W is decreased. Further, the plasma concentratesabove the wafer W with less diffusion, thereby reducing the dissociationspace. In this case, dissociation of a fluorocarbon family process gasis suppressed for the photo-resist film to be less etched. Accordingly,the application voltage from the variable DC power supply 50 ispreferably controlled by the controller 51, such that the length of theplasma sheath on the upper electrode 34 is increased to a level forforming desired pressed plasma. It should be noted that, also in thiscase, the application current or application power may be controlled inplace of the application voltage from the variable DC power supply 50.

Further, when the plasma is formed, electrons are generated near theupper electrode 34. When a DC voltage is applied from the variable DCpower supply 50 to the upper electrode 34, electrons are accelerated inthe vertical direction within the process space due to the potentialdifference between the applied DC voltage value and plasma potential. Inother words, the variable DC power supply 50 can be set at a desiredpolarity, voltage value, and current value, to irradiate thesemiconductor wafer W with electrons. The radiated electrons reform thecomposition of the mask or photo-resist film to reinforce the film.Accordingly, the application voltage value and application current valuefrom the variable DC power supply 50 can be used to control the quantityof electrons generated near the upper electrode 34 and the accelerationvoltage for accelerating the electrons toward the wafer W, so that thephoto-resist film is reinforced in a predetermined manner.

Particularly, where the photo-resist film on the semiconductor wafer Wis a photo-resist film (which will be referred to as an ArF resist film)for an ArF excimer laser (with a wavelength of 193 nm), the ArF resistfilm changes its polymer structure through reactions shown in thefollowing chemical formulas (1) and (2), and is then irradiated withelectrons, thereby arriving at the structure shown on the right side ofthe following chemical formula (3). In this case, by the irradiationwith electrons, the composition of the ArF resist film is reformed(resist cross-linkage reaction), as shown in a portion d of the chemicalformula (3). Since this portion d has a function of greatly enhancingthe etching resistance property (plasma resistance property), theetching resistance property of the ArF resist film remarkably increases.As a consequence, the surface roughness of the ArF resist film issuppressed, and the etching selectivity of an etching target layerrelative to the ArF resist film is increased.

Accordingly, the application voltage value or current value from thevariable DC power supply 50 is preferably controlled by the controller51 to enhance the etching resistance property of the photo-resist film(particularly, ArF resist film) by irradiation with electrons.

Further, as described above, when a DC voltage is applied to the upperelectrode 34, electrons generated near the upper electrode 34 in plasmageneration are accelerated in the vertical direction within the processspace. The polarity, voltage value, and current value of the variable DCpower supply 50 can be set at predetermined conditions, so thatelectrons reach into holes formed on the semiconductor wafer W. As aconsequence, the shading effect is suppressed to obtain a good processedshape without bowing, while improving the uniformity of the processedshape.

It is assumed that electron current amount I_(DC) due to the DC voltageis used as the quantity of electrons incident on the wafer W, where theacceleration voltage of electrons is controlled. In this case, whereI_(ion) is ion current amount incident on the wafer from plasma, it ispreferable to satisfy I_(DC)>(½)I_(ion). Since I_(ion)=Zρv_(ion)e(where, Z is charge number, ρ is current velocity density, v_(ion) ision velocity, and e is electron charge amount 1.6×10⁻¹⁹C), and ρ is inproportion to electron density Ne, I_(ion) is in proportion to Ne.

As described above, the DC voltage applied to the upper electrode 34 canbe controlled, so as to exercise the sputtering function onto the upperelectrode 34 and the plasma pressing function, as well as the supplyfunction of supplying a large quantity of electrons generated at theupper electrode 34 to the semiconductor wafer W, as described above.This arrangement makes it possible to reinforce the photo-resist film,supply optimum polymers, and suppress dissociation of the process gas.As a consequence, the surface roughness of the photo-resist issuppressed, and the etching selectivity of an etching target layerrelative to the photo-resist film is increased. Further, the CD of anopening portion formed in the photo-resist film is prevented fromexpanding, thereby realizing pattern formation with high accuracy.Particularly, these effects are more enhanced by controlling the DCvoltage to suitably exercise the three functions described above, i.e.,the sputtering function, plasma pressing function, and electron supplyfunction.

It should be noted that, it depends on process conditions or the like todetermine which one of the functions described above is predominant. Thevoltage applied from the variable DC power supply 50 is preferablycontrolled by the controller 51 to exercise one or more of the functionsto effectively obtain the corresponding effects.

Next, an explanation will be give of the result of a case where thefunctions described above were utilized to improve the selectivity of anSiO₂ film disposed as an etching target film relative to a photo-resistfilm. In this case, the electrode plate 36 of the upper electrode 34 wasmade of silicon, an RF power with a frequency of 60 MHz was applied at100 to 3,000 W from the first RF power supply 48 to the upper electrode34, an RF power with a frequency of 2 MHz was applied at 4,500 W fromthe second RF power supply 90 to the lower electrode or susceptor 16,and the etching gas was C₄F₆/Ar/O₂. Under these conditions, theapplication voltage from the variable DC power supply 50 was set atdifferent values to measure change in etching rates for the photo-resistfilm and SiO₂ film and change in selectivity of the SiO₂ film relativeto the photo-resist film. FIG. 5 shows the results. As shown in FIG. 5,as the absolute value of the negative DC voltage applied to the upperelectrode 34 increases, the selectivity of the SiO₂ film relative to thephoto-resist film becomes higher. Where the absolute value is largerthan that of −600V, the selectivity rapidly increases. Accordingly, ithas been confirmed that the selectivity of the SiO₂ film relative to thephoto-resist film is remarkably improved where a negative DC voltagewith an absolute value larger than that of −600V is applied to the upperelectrode 34.

The DC voltage applied to the upper electrode 34 can be adjusted tocontrol the plasma potential. In this case, etching by-products can beprevented from being deposited on the upper electrode 34, the depositionshield 11 forming a part of the chamber wall, the inner wall member 26,and the insulating shield member 42.

If etching by-products are deposited on the upper electrode 34 or thedeposition shield 11 forming the chamber wall, a problem may arise inthat the process characteristics change or particles are generated.Particularly, there is involving sequentially etching a multi-layeredfilm, such as that shown in FIG. 6, in which an Si-organic film (SiOC)101, SiN film 102, SiO₂ film 103, and photo-resist 104 are laminated ona semiconductor wafer W in this order. In this case, since suitableetching conditions are different for the respective films, a memoryeffect may occur in that a previous process leaves some effect thataffects a subsequent process.

The amount of deposition of etching by-products described above dependson the potential difference between the plasma and the upper electrode34, chamber wall, or the like. Accordingly, deposition of etchingproducts can be suppressed by controlling the plasma potential.

FIG. 7 is a view showing change in plasma potential waveforms where a DCvoltage is applied to the upper electrode 34. FIG. 8 is a view showingthe relationship between the DC voltage value applied to the upperelectrode and the maximum value of the plasma potential. As shown inFIGS. 7 and 8, where a negative DC voltage is applied to the upperelectrode 34, the maximum value of the plasma potential becomes lowerwith increase in the absolute value of the voltage. Accordingly, theplasma potential can be controlled by the DC voltage applied to theupper electrode 34. This is so, because, where the upper electrode 34 issupplied with a DC voltage with an absolute value larger than a selfbias (V_(dc)) obtained by an RF power applied to the upper electrode 34,the absolute value of V_(dc) becomes larger, thereby lowering the plasmapotential. More specifically, the value of the plasma potential has beendetermined by raise given by the upper electrode to the plasmapotential. However, where a negative voltage with a high absolute valueis applied to the upper electrode, the entire voltage amplitude on theupper electrode comes into the negative potential side. In this case,the plasma potential is determined by the potential of the wall, andthus becomes lower.

As described above, the voltage applied from the variable DC powersupply 50 to the upper electrode 34 can be controlled to lower theplasma potential. As a consequence, etching by-products can be preventedfrom being deposited on the upper electrode 34, the deposition shield 11forming a part of the chamber wall, and the insulating members (members26 and 42) inside the chamber 10. The plasma potential Vp is preferablyset at a value within a range of 80V≦Vp≦200V.

Further, the DC voltage applied to the upper electrode 34 can becontrolled to effectively exercise the plasma potential controlfunction, in addition to the sputtering function onto upper electrode34, plasma pressing function, and electron supply function, as describedabove.

Further, the applied DC voltage contributes to formation of plasma, asanother effect obtained by the DC voltage applied to the upper electrode34. In this case, the plasma density can be higher and the etching rateis thereby increased.

This is so, because, the negative DC voltage applied to the upperelectrode hinders electrons from entering the upper electrode and thussuppresses extinction of electrons. Further, where the negative DCvoltage accelerates ions onto the upper electrode, electrons are emittedfrom the electrode. These electrons are accelerated at a high velocitydue to the difference between the plasma potential and applicationvoltage value, and ionize neutral gas (turn the gas into plasma),thereby increasing the electron density (plasma density).

Further, when plasma is generated, the DC voltage applied to the upperelectrode 34 from the variable DC power supply 50 relatively increasesthe plasma density at the central portion due to plasma diffusion. Wherethe pressure inside the chamber 10 is high and the etching gas is anegative gas, the plasma density tends to be lower at the centralportion of the chamber 10. However, since the DC voltage applied to theupper electrode 34 increases the plasma density at the central portion,the plasma density can be controlled to perform uniform etching. Itshould be noted that, since the etching characteristics cannot bedefined only by the plasma density, a plasma density with higheruniformity does not necessarily improve the etching uniformity.

The reason for this will be explained, with reference to experiments.

In the apparatus shown in FIG. 1, a semiconductor wafer was loaded intothe chamber and placed on the susceptor, and a BARC (organicanti-reflection film) and an etching target film were etched. When theBARC was etched, the first RF power was set at 2,500 W, the second RFpower was set at 2,000 W, and the process gas employed was CH₂F₂, CHF₃,Ar, and O₂. When the etching target film was etched to form a hole, thefirst RF power was set at 1,500 W, the second RF power was set at 4,500W, and the process gas employed was CH₄F₆, CF₄, Ar, and O₂. At thistime, the DC voltage applied to the upper electrode was set at differentvalues of −800V, −1,000V, and −1,200V. FIG. 9 shows distributions ofelectron density (plasma density) in the radial direction obtained inthis case. As shown in FIG. 9, as the absolute value of the DC voltageincreases from −800V to −1,200V, the electron density increases at thecenter, which improves the plasma density uniformity. FIGS. 10A to 10Cschematically show etched shapes at the center and edge obtained in thiscase. As shown in FIGS. 10A to 10C, as the DC voltage changes from −800Vto −1,000V, the etching uniformity is improved. On the other hand, asthe DC voltage changes from −1,000V to −1,200V, although the electrondensity uniformity is improved, the etching performance becomes too highat the center and thus the etching uniformity is deteriorated.Accordingly, it has been confirmed that the etching uniformity is thebest at −1,000V. In any case, the DC voltage can be adjusted to performuniform etching.

As described above, the DC voltage applied to the upper electrode 34 canbe controlled to effectively exercise at least one of theabove-described sputtering function onto the upper electrode 34, plasmapressing function, electron supply function, plasma potential controlfunction, electron density (plasma density) increase function, andplasma density control function.

The variable DC power supply 50 may be formed of the one that can applya voltage within a range of −2,000 to +1,000V. In order to effectivelyexercise the various functions described above, the application DCvoltage from the variable DC power supply 50 is preferably set to havean absolute value of 500V or more.

Further, the application DC voltage is preferably a negative voltagewith an absolute value larger than the self-bias voltage generated onthe surface of the upper electrode by the first RF power applied to theupper electrode 34.

An explanation will be given of an experiment performed to confirm thismatter. FIG. 11 is a graph showing the relationship between theself-bias voltage V_(dc) generated on the surface of the upper electrode34 and the DC voltage applied to the upper electrode 34, where the RFpower for plasma generation (60 MHz) applied from the first RF powersupply 48 to the upper electrode 34 is set at different power values. Inthis case, the self-bias voltage V_(dc) generated on the surface of theupper electrode 34 was measured while plasma was generated under thefollowing conditions. Specifically, the pressure inside the chamber wasset at 2.7 Pa, the RF power applied to the upper electrode 34 atdifferent values of 650 W, 1,100 W, and 2,200 W, the RF power applied tothe lower electrode or susceptor 16 at 2,100 W, the process gas flowrates of C₄F₆/Ar/O₂ at 25/700/26 mL/min, the distance between the upperand lower electrodes at 25 mm, the back pressure (central portion/edgeportion) at 1,333/4,666 Pa, the temperature of the upper electrode 34 at60° C., the sidewall temperature of the chamber 10 at 50° C., and thetemperature of the susceptor 16 at 0° C.

As shown in the graph of FIG. 11, the application DC voltage iseffective where it is higher than the self-bias voltage V_(dc) on theupper electrode 34, and, as the RF power applied to the upper electrode34 is higher, the generated negative self-bias voltage V_(dc) is larger.Accordingly, the application DC voltage is required to be a negativevoltage with an absolute value larger than the self-bias voltage V_(dc)generated by the RF power. To reiterate, it has been confirmed that theDC voltage applied to the upper electrode 34 is preferably set to havean absolute value at least larger than the self-bias voltage V_(dc)generated on the upper electrode.

Further, as shown in FIG. 12, a detector 55 for detecting the state ofplasma through, e.g., a plasma detection window 10 a may be disposed forthe controller 51 to control the variable DC power supply 50 based onthe detection signal, so that the DC voltage applied to the upperelectrode 34 can be automatically adjusted to effectively exercise thefunctions described above. Furthermore, a detector for detecting thesheath length or a detector for detecting the electron density may bedisposed for the controller 51 to control the variable DC power supply50 based on the detection signal.

Where the plasma etching apparatus according to this embodiment is usedto etch an insulating film (for example, a Low-k film) disposed on awafer W, the following combination of gases is particularly preferablyused as a process gas.

Specifically, where over etching is performed under via-etchingconditions, a combination of C₅F₈, Ar, and N₂ may be preferably used asa process gas. In this case, the selectivity of an insulating filmrelative to an underlying film (SiC, SiN, etc.) can become larger.

Alternatively, where trench etching conditions are used, CF₄ or acombination of (C₄F₈, CF₄, Ar, N₂, and O₂) may be preferably used as aprocess gas. In this case, the selectivity of an insulating filmrelative to a mask can become larger.

Alternatively, where HARC etching conditions are used, a combination of(C₄F₆, CF₄, Ar, and O₂), (C₄F₆, C₃F₈, Ar, and O₂), or (C₄F₆, CH₂F₂, Ar,and O₂) may be preferably used as a process gas. In this case, theetching rate of an insulating film can become higher.

The process gas is not limited to the examples described above, andanother combination of (CxHyFz gas/additive gas such as N₂ orO₂/dilution gas) may be used.

Incidentally, where a DC voltage is applied to the upper electrode 34,electrons may accumulate on the upper electrode 34 and thereby causeabnormal electric discharge between the upper electrode 34 and the innerwall of the chamber 10. In order to suppress such abnormal electricdischarge, this embodiment includes the GND block (conductive member) 91as a part grounded in the sense of DC, which is disposed on thedeposition shield 11 that constitutes the chamber wall. The GND block 91is exposed to plasma, and is electrically connected to a conductiveportion in the deposition shield 11. The DC voltage current applied fromthe variable DC power supply 50 to the upper electrode 34 flows throughthe process space to the GND block 91, and is then grounded through thedeposition shield 11. The GND block 91 is made of a conductor, andpreferably a silicon-containing substance, such as Si or SiC. The GNDblock 91 may be preferably made of C. The GND block 91 allows electronsaccumulated in the upper electrode 34 to be released, thereby preventingabnormal electric discharge. The GND block 91 preferably has aprotruding length of 10 mm or more.

Further, in order to prevent abnormal electric discharge, it may beeffective to use a method of superposing very short periodic pulses ofthe opposite polarity, as shown in FIG. 13, by a suitable means, withthe DC voltage applied to the upper electrode 34, so as to neutralizeelectrons.

The position of the GND block 91 is not limited to that shown in FIG. 1,as long as it is disposed in the plasma generation area. For example, asshown in FIG. 14, the GND block 91 may be disposed on the susceptor 16side, e.g., around the susceptor 16. Alternatively, as shown in FIG. 15,the GND block 91 may be disposed near the upper electrode 34, e.g., as aring disposed outside the upper electrode 34. However, when plasma isgenerated, Y₂O₃ or a polymer that covers the deposition shield 11 or thelike flies out and may be deposited on the GND block 91. In this case,the GND block 91 cannot maintain the grounding performance any more inthe sense of DC, and thus hardly exercises the effect of preventingabnormal electric discharge. Accordingly, it is important to preventsuch deposition. For this reason, the GND block 91 is preferably locatedat a position remote from members covered with Y₂O₃ or the like, butpreferably near parts made of an Si-containing substance, such as Si orquartz (SiO₂). For example, as shown in FIG. 16A, an Si-containingmember 93 is preferably disposed near the GND block 91. In this case,the length L of a portion of the Si-containing member 93 below the GNDblock 91 is preferably set to be equal to or longer than the protrudinglength M of the GND block 91. Further, in order to prevent the functionfrom being deteriorated due to deposition of Y₂O₃ or a polymer, as shownin FIG. 16B, it is effective to form a recess 91 a in the GND block 91where flying substances are hardly deposited. It is also effective toincrease the surface are of the GND block 91, so that it cannot beentirely covered with Y₂O₃ or a polymer. Further, in order to suppressdeposition, it is effective to increase the temperature. In thisrespect, the upper electrode 34 is supplied with an RF power for plasmageneration, and thus increases the temperature around it. Accordingly,the GND block 91 is preferably disposed near the upper electrode 34, asshown in FIG. 15, to increase the temperature and thereby preventdeposition. Particularly in this case, the GND block 91 is preferablydisposed as a ring outside the upper electrode 34, as shown in FIG. 15.

In order to more effectively remove the influence of deposition on theGND block 91, due to Y₂O₃ or a polymer flying out from the depositionshield 11 and so forth, it is effective to make a negative DC voltageapplicable to the GND block 91, as shown in FIG. 17. Specifically, wherea negative DC voltage is applied to the GND block 91, depositionsticking thereto is sputtered or etched, so as to clean the surface ofthe GND block 91. In the structure shown in FIG. 17, a switchingmechanism 53 is configured to switch the connection of the GND block 91between the variable DC power supply 50 and a ground line, so that avoltage can be applied to the GND block 91 from the variable DC powersupply 50. Further, a grounded conductive auxiliary member 91 b isdisposed to receive flow of a DC electron current generated by anegative DC voltage applied to the GND block 91. The switching mechanism53 includes a first switch 53 a to switch the connection of the variableDC power supply 50 between the matching unit 46 and GND block 91, and asecond switch 53 b to turn on/off the connection of the GND block 91 tothe ground line. In the structure shown in FIG. 17, the GND block 91 isdisposed as a ring outside the upper electrode 34, while the conductiveauxiliary member 91 b is disposed around the susceptor 16. Although thisarrangement is preferable, another arrangement may be adopted.

During plasma etching, the structure shown in FIG. 17 is typically setas shown in FIG. 18A, in which the first switch 53 a of the switchingmechanism 53 is connected to the upper electrode 34, so the variable DCpower supply 50 is connected to the upper electrode 34, while the secondswitch 53 b is in the ON-state, so the GND block 91 is connected to theground line. In this state, the first RF power supply 48 and variable DCpower supply 50 are electrically connected to the upper electrode 34,and plasma is thereby generated. At this time, a DC electron currentflows from the upper electrode 34 through plasma into the grounded GNDblock 91 and conductive auxiliary member 91 b (a positive ion currentflows in the opposite direction). In this case, the surface of the GNDblock 91 may be covered with deposition of Y₂O₃ or a polymer, asdescribed above.

Accordingly, cleaning is then performed to remove this deposition. Forthis cleaning, as shown in FIG. 18B, the first switch 53 a of theswitching mechanism 53 is switched to the GND block 91, and the secondswitch 53 b is turned off. In this state, the first RF power supply 48is electrically connected to the upper electrode 34, and cleaning plasmais thereby generated, while a negative DC voltage is applied from thevariable DC power supply 50 to the GND block 91. As a consequence, a DCelectron current flows from the GND block 91 into the conductiveauxiliary member 91 b. On the other hand, positive ions flow into theGND block 91. Accordingly, the DC voltage can be adjusted to control theenergy of positive ions incident on the GND block 91, so that thesurface of the GND block 91 is sputtered by ions to remove depositionsticking to the surface of the GND block 91.

Further, as shown in FIG. 19, the second switch 53 b may be set in theOFF state during a partial period of plasma etching, so that the GNDblock 91 is in a floating state. At this time, a DC electron currentflows from the upper electrode 34 through plasma into the conductiveauxiliary member 91 b (a positive ion current flows in the oppositedirection). In this case, the GND block 91 is given a self bias voltage,which provides energy for positive ions to be incident on the GND block91, thereby cleaning the GND block 91.

During the cleaning described above, the application DC voltage can besmall, and thus the DC electron current is also small at this time.Accordingly, in the structure shown in FIG. 17, where electric chargesdue to leakage current can be prevented from accumulating in the GNDblock 91, the conductive auxiliary member 91 b is not necessarilyrequired.

In the structure shown in FIG. 17, for cleaning, the connection of thevariable DC power supply 50 is switched from the upper electrode 34 tothe GND electrode 91, so that a DC electron current due to applicationof a DC voltage flows from the GND block 91 to the conductive auxiliarymember 91 b. Alternatively, it may be adopted that the positive terminalof the variable DC power supply 50 is connected to the upper electrode34, while the negative terminal is connected to the GND block 91, sothat a DC electron current due to application of a DC voltage flows fromthe GND block 91 to the upper electrode 34. In this case, the conductiveauxiliary member is not necessary. FIG. 20 shows such a structure. Thestructure shown in FIG. 20 includes a connection switching mechanism 57,which is configured to perform connection switching such that, duringplasma etching, the negative terminal of the variable DC power supply 50is connected to the upper electrode 34, while the GND block 91 isconnected to the ground line. Further, in this switching, duringcleaning, the positive terminal of the variable DC power supply 50 isconnected to the upper electrode 34, while the negative terminal isconnected to the GND block 91. This connection switching mechanism 57includes a first switch 57 a to switch the connection of the variable DCpower supply 50 to the upper electrode 34 between the positive terminaland negative terminal, a second switch 57 b to switch the connection ofthe variable DC power supply 50 to the GND block 91 between the positiveterminal and negative terminal, and a third switch 57 c to set thepositive terminal or negative terminal of the variable DC power supply50 to be grounded. The first switch 57 a and second switch 57 b arearranged to form an interlock switch structure. Specifically, when thefirst switch 57 a is connected to the positive terminal of the variableDC power supply 50, the second switch 57 b is connected to the negativeterminal of the DC power supply. Further, when the first switch 57 a isconnected to the negative terminal of the variable DC power supply 50,the second switch 57 b is set in the OFF state.

During plasma etching, the structure shown in FIG. 20 is set as shown inFIG. 21A, in which the first switch 57 a of the connection switchingmechanism 57 is connected to the negative terminal of the variable DCpower supply 50, so the negative terminal of the variable DC powersupply 50 is connected to the upper electrode 34. Further, the secondswitch 57 b is connected to the positive terminal of the variable DCpower supply 50, and the third switch 57 c is connected to the positiveterminal of the variable DC power supply 50 (the positive terminal ofthe variable DC power supply 50 is grounded), so that the GND block 91is connected to the ground line. In this state, the first RF powersupply 48 and variable DC power supply 50 are electrically connected tothe upper electrode 34, and plasma is thereby generated. At this time, aDC electron current flows from the upper electrode 34 through plasmainto the grounded GND block 91 (a positive ion current flows in theopposite direction). In this case, the surface of the GND block 91 maybe covered with deposition of Y₂O₃ or a polymer, as described above.

On the other hand, for cleaning, as shown in FIG. 21B, the first switch57 a of the connection switching mechanism 57 is switched to thepositive terminal of the variable DC power supply 50, the second switch57 b is switched to the negative terminal of the variable DC powersupply 50, and the third switch 57 c is set to be in a disconnectedstate. In this state, the first RF power supply 48 is electricallyconnected to the upper electrode 34, and cleaning plasma is therebygenerated, while a DC voltage is applied to the GND block 91 from thenegative terminal of the variable DC power supply 50 and to the upperelectrode 34 from the positive terminal of the variable DC power supply50. Due to the potential difference between these members, a DC electroncurrent flows from the GND block 91 into the upper electrode 34, whilepositive ions flow into the GND block 91. Accordingly, the DC voltagecan be adjusted to control the energy of positive ions incident on theGND block 91, so that the surface of the GND block 91 is sputtered byions to remove deposition sticking to the surface of the GND block 91.In this case, the variable DC power supply 50 appears to be in afloating state, but, in general, a power supply is provided with a frameground line, thus is safe.

In the example described above, although the third switch 57 c is in thedisconnected state, the positive terminal of the variable DC powersupply 50 may be kept in the connected state (the positive terminal ofthe variable DC power supply 50 is grounded). In this state, the firstRF power supply 48 is electrically connected to the upper electrode 34,and cleaning plasma is thereby generated, while a DC voltage is appliedfrom the negative terminal of the variable DC power supply 50 to the GNDblock 91. As a consequence, a DC electron current flows from the GNDblock 91 into the upper electrode 34 through plasma, while positive ionsflow into the GND block 91. Also in this case, the DC voltage can beadjusted to control the energy of positive ions incident on the GNDblock 91, so that the surface of the GND block 91 is sputtered by ionsto remove deposition sticking to the surface of the GND block 91.

In the examples shown in FIGS. 17 and 20, although a DC voltage isapplied to the GND block 91 during cleaning, an AC voltage may bealternatively applied. Further, in the example shown in FIG. 17,although the variable DC power supply 50 for applying a DC voltage tothe upper electrode is used for applying a voltage to the GND block 91,another power supply may be used for applying the voltage. Furthermore,in the examples shown in FIGS. 17 and 20, although the GND block 91 isgrounded during plasma etching, while a negative DC voltage is appliedto the GND block 91 during cleaning, this is not limiting. For example,during plasma etching, a negative DC voltage may be applied to the GNDblock 91. The term, “during cleaning” may be replaced with “duringashing” in the explanation described above. Furthermore, where thevariable DC power supply 50 is formed of a bipolar power supply, it doesnot require any complex switching operation, such as that of theconnection switching mechanism 57 described above.

The switching operations of the switching mechanism 53 of the exampleshown in FIG. 17 and the connection switching mechanism 57 of theexample shown in FIG. 20 are performed in accordance with commands sentfrom the control section 95.

In order to simply prevent the GND block 91 from losing the groundingperformance in the sense of DC, due to deposition of Y₂O₃ or a polymeron the GND block 91 in plasma generation, it is effective to partlycover the GND block 91 with another member, and to move them relative toeach other so as to expose a new surface of the GND block 91.Specifically, the arrangement shown in FIG. 22 may be adopted, in whichthe GND block 91 is set to have a relatively large area, and the surfaceof the GND block 91 to be in contact with plasma is partly covered witha mask member 111 movable in the arrow direction. This cover plate 111is movable, so that a portion to be exposed to plasma can be changed onthe surface of the GND block 91. In this case, although a drivingmechanism disposed in the chamber 10 may cause a problem about particlegeneration, it cannot be serious because the frequency of use of thedriving mechanism is as low as once in 100 hours. Further, for example,the arrangement shown in FIG. 23 may be effective, in which a columnarGND block 191 is rotatably disposed, and the outer periphery surface ofthe GND block 191 is covered with a mask member 112, so that it ispartially exposed. Where the GND block 191 is rotated, the portion to beexposed to plasma can be changed. In this case, a driving mechanism maybe disposed outside the chamber 10. Each of the mask members 111 and 112may be formed of a member having a high plasma resistance property, suchas an aluminum plate covered with a ceramic, such as Y₂O₃, formed bythermal spray.

In order to simply prevent the GND block 91 from losing the groundingperformance in the sense of DC due to deposition, it is also effectiveto partly cover the GND block 91 with another member, which is to begradually etched by plasma, so that a part of the surface of the GNDblock 91, which has not lost conductivity, is always exposed. Forexample, the arrangement shown in FIG. 24A may be adopted, in which thesurface of the GND block 91 is partly covered with a stepped cover film113 disposed to leave an initially exposed surface 91 c that provides agrounding performance. In this case, after a plasma process is performedfor, e.g., 200 hours, the initially exposed surface 91 c of the GNDblock 91 loses conductivity, as shown in FIG. 24B. However, the steppedcover film 113 is designed to have a thin portion such that it has beenetched by this time, so that a new exposed surface 91 d of the GND block91 appears. The new exposed surface 91 d provides a groundingperformance. This cover film 113 has the effect of preventing a wallsurface material from being deposited on the GND block 91, as well asthe effect of reducing ions incident on the GND block 91 to preventcontamination thereof.

In practical use, as shown in FIG. 25, it is preferable to use a coverfilm 113 a in which a number of thin layers 114 are stacked while thelayers are gradually shifted. In this case, where one layer 114disappears due to etching by plasma in a time Te, and an exposed surfaceof the GND block 91 loses conductivity due to contamination in a timeTp, the thickness of the layer 114 is set to satisfy Te<Tp, so that aconductive surface is always ensured on the GND block 91. The number oflayers 114 is preferably set to make the service life of the GND block91 longer than the frequency of maintenance. Further, in order toimprove the maintenance performance, one layer 114 a is provided with adifferent color from the others, as shown in FIG. 25, so that it ispossible to know the time to replace the GND block 91 with a new one, bythis film 114 a, for example, when the surface area of this film 114 aexceeds a certain value.

Each of the cover films 113 and 113 a is preferably formed of a film tobe suitably etched by plasma, such as a photo-resist film.

In order to simply prevent the GND block 91 from losing the groundingperformance in the sense of DC due to deposition, it may be also adoptedto dispose a plurality of GND blocks 91, so that they are switched inturn to exercise a grounding performance. For example, as shown in FIG.26, three GND blocks 91 are disposed and only one of them is selectivelygrounded by a shift switch 115. Further, a current sensor 117 isdisposed on a common ground line 116 to monitor a DC current flowingtherethrough. The current sensor 117 is used to monitor a currentflowing through a grounded GND block 91, and when the current valuebecomes lower than a predetermined value, it is determined that this GNDblock 91 cannot exercise the grounding performance, and thus theconnection is switched from this one to another GND block 91. The numberof GND blocks 91 is suitably selected from a range of about 3 to 10.

In the example described above, a GND block not grounded is in anelectrically floating state, but such a GND block may be supplied withan electric potential for protection to protect a GND block in an idlestate, in place of use of the shift switch 115. FIG. 27 shows an exampledesigned in this aspect. As shown in FIG. 27, each of ground lines 118respectively connected to GND blocks 91 is provided with a variable DCpower supply 119. In this case, the voltage of a GND block 91 toexercise a grounding performance is set at 0V by controlling the voltageof the corresponding variable DC power supply 119. Further, the voltageof each of the other GND blocks 91 is set at, e.g., 100V to prevent anelectric current from flowing therethrough by controlling the voltage ofthe corresponding variable DC power supply 119. When the current valuedetected thereby becomes lower than a predetermined value at the currentsensor 117 on the ground line 118 connected to a GND block 91 toexercise a grounding performance, it is determined that this GND block91 cannot exercise the grounding performance. Accordingly, the voltageof the variable DC power supply 119 corresponding to another GND block91 is controlled to be a value for this GND block 91 to exercise agrounding performance.

As described above, where the application voltage from a DC power supply119 is set at a negative value of about −1 kV, the GND block 91connected thereto can function as an electrode to apply a DC voltage toplasma. However, if this value is too large, the plasma is affected.Further, the voltage applied to the GND block 91 can be controlled toobtain a cleaning effect on the GND block 91.

Next, a detailed explanation will be given of plasma obtained bysuperposing the RF power and DC voltage applied to the upper electrode34, according to this embodiment.

FIG. 28 is a view showing the electron temperature distribution ofplasma, where the horizontal axis denotes the electron temperature andthe vertical axis denotes the plasma intensity. In order to obtain highdensity plasma, it is effective to use an RF power with a relativelyhigh frequency that ions cannot follow, such as 13.56 MHz or more, asdescribed above. However, in the case of the electron temperaturedistribution of plasma (RF plasma) obtained by an RF power application,an intensity peak appears within an excitation domain having lowerelectron temperature, as indicated by a line A (case A) in FIG. 28. Asthe power is increased to obtain a higher plasma density, the intensitybecomes higher within a dissociation domain having middle electrontemperature. As a consequence, dissociation of a fluorocarbon gas(CxFy), such as C₄F₈ gas, used as the etching process gas, proceeds,thereby deteriorating etching characteristics.

On the other hand, the electron temperature distribution of plasma (DCplasma) obtained by a DC voltage application is indicated by a line B(case B) in FIG. 28. In this case, the plasma density is almost equal tothat corresponding to the line A (case A), but an intensity peak appearswithin an ionization domain having higher electron temperature, whileessentially no distribution part is present within the excitation domainor dissociation domain. Where a DC voltage is superposed on an RF powerof 13.56 MHz or more, a high plasma density can be obtained withoutincreasing the power level of the RF power. Further, the plasma thusformed is polarized such that the electron temperature has intensitypeaks within the excitation domain and ionization domain. This bringsabout ideal plasma that can reduce dissociation of the process gas withthe same plasma density.

This arrangement will be specifically explained further with referenceto FIG. 29. FIG. 29 is a view showing the electron temperaturedistribution of plasma obtained by solely using an RF power, incomparison with that obtained by superposing a DC voltage on an RFpower. In FIG. 29, a line C shows a case where an RF power with afrequency of 60 MHz was applied at 2,400 W to the upper electrode 34,while an RF power with a frequency of 2 MHz for attracting ions wasapplied at 1,000 W to the lower electrode or susceptor 16. On the otherhand, a line D shows a case where RF powers of 60 MHz and 2 MHz werealso respectively applied to the upper electrode 34 and susceptor 16,and a DC voltage was further applied to the upper electrode 34. In thecase of the line D, the RF power and DC voltage applied to the upperelectrode 34 were respectively set at 300 W and −900V to obtain the sameplasma density as that of the case of the line C. As shown in FIG. 29,where the DC voltage is superposed, high density plasma is formed atthis same density while being polarized with almost no part of theelectron temperature distribution within the dissociation domain. Inthis case, the electron temperature distribution can be controlled toobtain a more suitable plasma state by changing the frequency and powerlevel of the RF power and the value of the DC voltage, both of which areapplied to the upper electrode 34.

As described above, as the frequency of the RF power applied to theupper electrode 34 is lower, the plasma has a higher energy and V_(dc)is increased. In this case, dissociation of the process gas is promoted,thus the control margin concerning the DC voltage application becomesnarrower. However, where the frequency of the RF power applied to theupper electrode 34 is set at 40 MHz or more, e.g., 60 MHz, the plasmahas a lower energy, and thus the control margin concerning the DCvoltage application becomes broader. Accordingly, the frequency of theRF power applied to the upper electrode 34 is preferably set at 40 MHzor more.

Next, an explanation will be given of a bias RF power for attractingions, applied to the lower electrode or susceptor 16. The RF powerapplied from second RF power supply 90 to the susceptor 16 is a bias RFpower for attracting ions, which can provide different effects dependingon whether the frequency (RF application frequency) is less than 10 MHzor 10 MHz or more. Specifically, where the RF application frequency isless than 10 MHz, e.g., 2 MHz, ions can follow the RF applicationfrequency, in general. In this case, as shown in FIG. 30A, the ionenergy incident on the wafer corresponds to the wafer potential, whichvaries in accordance with the RF power voltage waveform. On the otherhand, where the bias RF frequency is 10 MHz or more, e.g., 13.56 MHz,ions cannot follow the RF application frequency, in general. In thiscase, as shown in FIG. 30B, the ion energy incident on the wafer dependsnot on the wafer potential, but on V_(dc). In the case of a frequency(e.g., 2 MHz) that ions can follow, as shown in FIG. 30A, the ionmaximum energy corresponds to Vpp. Further, at a portion where thedifference between the plasma potential and wafer potential is smaller,the ion energy becomes smaller. In this case, as indicated by a line Ein the ion energy distribution shown in FIG. 31, the ion energy on thewafer is polarized and broader. On the other hand, in the case of afrequency (e.g., 13.56 MHz) that ions cannot follow, as shown in FIG.30B, the ion energy corresponds to V_(dc) without reference to the waferpotential. In this case, as indicated by a line F in FIG. 31, the ionenergy on the wafer takes on the maximum value near a portioncorresponding to V_(dc), while almost no ions have a higher energy thanV_(dc).

Accordingly, a frequency of less than 10 MHz that ions can follow issuitable where higher ion energy is required to increase productivity.On the other hand, a frequency of 10 MHz or more that ions cannot followis suitable where lower ion energy is required, such as a case where thesurface roughness of a mask is critical. Accordingly, the frequency ofthe bias RF power is preferably selected in accordance with the intendedpurpose.

In the examples described above, a DC voltage is applied to exercise thesputtering function on the upper electrode 34, plasma pressing function,electron supply function, and so forth, but an AC voltage can providethe same effects. However, the frequency of the AC voltage is set to besmaller than the frequency of an RF power for plasma generation. Ineither of the cases using the DC voltage and AC voltage, the voltage maybe pulsed or modulated, such as AM modulation or FM modulation.

Incidentally, there is a case where a low dielectric constant barrierlayer made of SiC is used as an underlying etching-stopper layer to etcha Low-k film or etching target layer on the upper side. According to theprior art, it is difficult to ensure a sufficient etching selectivity atthis time. In this respect, the plasma etching apparatus according tothis embodiment is used to perform etching, while a DC voltage issuperposed with a first RF power applied to the upper electrode 34, soas to effectively exercise the functions described above. As aconsequence, a Low-k film, such as an SiOC film, used as an insulatingfilm can be etched at a high etching selectivity relative to anunderlying etching-stopper layer.

FIGS. 32A and 32B show a wafer sectional structure used as a typicaletching target in this etching. As shown in FIG. 32A, this wafer Wincludes an underlying film or SiC layer 201, an insulating film or SiOCfamily film 202, an SiO₂ film 203, and an anti-reflection film or BARC204 stacked from the under side in this order. Further, an etching maskor ArF resist 205 patterned in a predetermined shape is disposed on theanti-reflection film 204. The SiOC family film 202 is a Low-k filmcontaining Si, O, C, and H as components, the representatives of whichare, e.g., SiLK (Trade name; Dow Chemical Ltd.), MSQ of SOD-SiOCH(methyl-silsesqui-siloxane), CORAL of CVD-SiOCH (Trade name; NovellusSystems Ltd.), and Black Diamond (Trade name; Applied Materials Ltd.).In place of the SiOC family film 202, the etching target may be anotherLow-k film, such as an organic Low-k film, e.g., a PAE family film, HSQfamily film, PCB family film, or CF family film; or an inorganic Low-kfilm, e.g., an SiOF family film.

The underlying film or SiC layer 101 may be formed of, e.g., BLOk (Tradename; Applied Materials Ltd.).

As shown in FIG. 32B, this wafer W is etched by plasma of a fluorocarbon(CF family) gas to form a recess (trench or hole) 211 in accordance withthe mask pattern of the ArF resist 205. In this plasma etching, a DCvoltage is superposed to the upper electrode 34 to ensure a sufficientselectivity between the underlying layer or SiC layer 201 and theetching target layer or SiOC family film 202. In this case, the DCvoltage applied from the variable DC power supply 50 to the upperelectrode 34 is preferably set to be 0 to −1,500V. Further, the etchingconditions are preferably set as follows: for example, the pressureinside the chamber=1.3 to 26.7 Pa; RF power (upper electrode/lowerelectrode)=0 to 3,000 W/100 to 5,000 W; the process gas=a mixture gas ofC₄F₈, N₂, and Ar; the flow-rate ratio of C₄F₈/N₂/A=4 to 20/100 to500/500 to 1,500 mL/min.

In an experiment, a sample of a multi-layer structure was prepared, asshown in FIG. 32A, and etched by the apparatus shown in FIG. 1. Usingthe ArF resist 205 having a via (hole) pattern as a mask, the SiOCfamily film 202 was etched until the underlying film or SiC layer 201was exposed, to form a via. The etching was performed under thefollowing etching conditions 1 and 2, and comparison was made in etchingcharacteristics between a case where a DC voltage of −900V was appliedto the upper electrode 34 (present examples 1 and 2), and a case whereno DC voltage was applied (comparative examples 1 and 2). Table 1 showsthe results.

<Etching Conditions 1>

Pressure inside the chamber=6.7 Pa;

RF power (upper electrode/lower electrode)=400 W/1,500 W;

Process gas flow rates of C₄F₈/Ar/N₂=6/1,000/180 mL/min;

Distance between the upper and lower electrodes=35 mm;

Process time=25 to 35 seconds;

Back pressure (helium gas: central portion/edge portion)=2,000/5,332 Pa;

Upper electrode 34 temperature=60° C.;

Chamber 10 sidewall temperature=60° C.; and

Susceptor 16 temperature=0° C.

<Etching Conditions 2>

The conditions were set to be the same as those of the etchingconditions 1 except for RF power (upper electrode/lower electrode)=800W/2,500 W.

As shown in Table 1, in either of the cases using the etching conditions1 and the etching conditions 2, the present examples 1 and 2 with a DCvoltage of −900V applied to the upper electrode 34 greatly improved bothof the selectivity relative to SiC and the selectivity relative toresist, as compared with the comparative examples 1 and 2 with no DCvoltage application, under the same conditions.

Further, in these cases, the etching rate was remarkably improved whilethe CD

(Critical Dimension) at the via top portion was prevented fromexpanding. According to the conventional etching technique, it isdifficult to realize both of improvement in the etching rate and controlof the CD (i.e., preventing CD expansion). By contrast, it has beenconfirmed that the application of a DC voltage described above canrealize both of them.

TABLE 1 Comparative Present example 1 example 1 (DC 0 V) (DC −900 V)Etching SiOC etching rate 262 433 conditions 1 (nm/min) Selectivityrelative 4.8 15.1 to SiC CD (nm) 153 149 Selectivity relative 3.4 96.3to resist Comparative Present example 2 example 2 (DC 0 V) (DC −900 V)Etching SiOC etching rate 487 589 conditions 2 (nm/min) Selectivityrelative 2.9 6.3 to SiC CD (nm) 153 141 Selectivity relative 6.6 11.9 toresist

TABLE 2 Power on upper side (W) 200 400 800 Etching rate 229 433 436(nm/min) Selectivity 33.8 15.1 9.3 relative to SiC CD (nm) 151 149 155Selectivity 10.2 96.3 7.1 relative to resist

Further, it has also been confirmed from comparison between theconditions 1 and conditions 2 in this Table 1, that the effect ofimproving the selectivity relative to SiC obtained by superposing a DCvoltage to the upper electrode 34 can be enhanced where the RF power(upper electrode/lower electrode) is smaller.

Then, using the etching conditions 1 or etching conditions 2 asreferences, some of the conditions were changed and etchingcharacteristics thus obtained were examined.

Table 2 shows etching characteristics obtained by changing the RF powerapplied to the upper electrode 34 with reference to the etchingconditions 1. As shown in this Table 2, the etching rate was improvedwhile the selectivity relative to SiC became smaller, with increase inthe RF power applied to the upper electrode 34. On the other hand, underthese conditions, change in the RF power applied to the upper electrode34 less affected the CD, and the selectivity relative to resist wasprominently excellent when the RF power was 400 W. Judging from theresult described above, it has been confirmed that the RF power appliedto the upper electrode 34 is preferably set at a value within a range ofabout 200 to 800 W.

Table 3 shows etching characteristics obtained by changing the RF powerapplied to the lower electrode or susceptor 16 with reference to theetching conditions 2. As shown in this Table 3, the etching rate wasgreatly improved while the selectivity relative to SiC tended to be lessimproved, with increase in the RF power applied to the lower electrode(susceptor 16). On the other hand, under these conditions, change in theRF power applied to the lower electrode less affected the CD, and theselectivity relative to resist was improved with increase in the RFpower. Judging from the result described above, it has been confirmedthat the RF power applied to the lower electrode is preferably set at avalue within a range of about 1,500 to 3,800 W.

Table 4 shows etching characteristics obtained by changing the processpressure with reference to the etching conditions 2. As shown in thisTable 4, the etching rate decreased and the etching was thereby stoppedwhere the process pressure was set to be too high under the etchingconditions 2 in which the RF power (upper electrode/lower electrode) wasas relatively large as 800/2,500 W. Accordingly, it has been confirmedthat the process pressure is preferably set at a value within a range ofabout 4 to 20 Pa.

Further, in light of the result shown in Table 4 as well as the resultsshown in Tables 2 and 3, it is thought preferable that the etching rateand the selectivity relative to SiC obtained by superposing a DC voltageare controlled by adjusting the RF power.

TABLE 3 Power on lower side (W) 1,500 2,500 3,800 Etching rate 436 589676 (nm/min) Selectivity 9.3 6.3 3.8 relative to SiC CD (nm) 155 141 157Selectivity 7.1 11.9 41 relative to resist

TABLE 4 Pressure (Pa) 4 6.7 20 Etching rate 394 589 154 (nm/min)Selectivity 3.8 6.3 Etching relative to SiC stop CD (nm) 151 141 6.3Selectivity 9.1 11.9 34.3 relative to resist

Table 5 shows etching characteristics obtained by changing the Ar flowrate with reference to the etching conditions 2. As shown in this Table5, although the influence of change in the Ar flow-rate ratio was notclear, the selectivity relative to SiC was improved by adding a certainamount of Ar, under the etching conditions 2 in which the RF power(upper electrode/lower electrode) was as relatively large as 800/2,500W. In this case, it has been confirmed that the Ar is preferably addedat 1,000 mL/min or less.

Then, a sample of a multi-layer structure was prepared, as shown in FIG.32A, and etched, using the ArF resist 205 having a line-and-space trenchpattern as a mask. In this case, the SiOC family film 202 was etcheduntil the underlying SiC layer 201 was exposed, to form a trench. Theetching was 2-step etching of main etching and over etching performedunder the following etching conditions, and comparison was made inetching characteristics between a case where a DC voltage of −900V wasapplied to the upper electrode 34 (a present example 3), and a casewhere no DC voltage was applied (a comparative example 3). Table 6 showsthe results.

<Main etching Conditions>

Pressure inside the chamber=26.7 Pa;

RF power (upper electrode/lower electrode)=300 W/1,000 W;

Process gas flow rates of CF₄/N₂/Ar/CHF₃=180/100/180/50 mL/min;

Distance between the upper and lower electrodes=35 mm;

Process time=10 seconds;

Back pressure (central portion/edge portion)=2,000/5,332 Pa;

Upper electrode 34 temperature=60° C.;

Chamber 10 sidewall temperature=60° C.; and

Susceptor 16 temperature=20° C.

<Over Etching Conditions>

Pressure inside the chamber=4.0 Pa;

RF power (upper electrode/lower electrode)=1,000 W/1,000 W;

Process gas flow rates of C₄F₈/N₂/Ar=6/260/1,000 mL/min;

Over etching amount=30%;

Distance between the upper and lower electrodes=35 mm; and

Other conditions are the same as the main etching conditions.

TABLE 5 Ar flow rate (mL/min) 0 300 600 1,000 Etching rate 574 646 574589 (nm/min) Selectivity 3.3 5.8 6.8 6.3 relative to SiC CD (nm) 153 149149 141 Selectivity 7.8 11.6 13.2 11.9 relative to resist

TABLE 6 Comparative Present example 3 example 3 (DC 0 V) (DC −900 V)SiOC etching rate 660.6 1104.6 (nm/min) Selectivity relative 11.7 15 toSiC CD (nm) 117 114.6 LER (nm) 7.64 4.88 Selectivity relative 2.3 3.1 toresist The SiOC etching rate and the selectivity relative to resist wereobtained only by the main etching step.

As shown in Table 6, in the case of the present example 3 with a DCvoltage of −900V applied to the upper electrode 34, the selectivityrelative to SiC was 15, which was greatly improved, as compared with thecomparative example 3 with no DC voltage application, in which theselectivity relative to SiC was 11.7.

Further, under the etching conditions described above, with a DC voltageof −900V applied to the upper electrode 34, not only the selectivityrelative to SiC, but also the selectivity relative to resist wasimproved, as shown in Table 6. Further, the etching rate of the SiOCfamily film 102 was greatly improved along with control to prevent theCD corresponding to the width of the trench from increasing. Further,the roughness of the line defining the etched trench (line etchingroughness; LER) became much lower.

In the examples described above, the SiOC family film 202 is etchedrelative to the underlying SiC layer 201, but the same effects describedabove can be obtained in another etching target. For example, thesectional structure shown in FIG. 33A includes a silicon substrate 206,on which a silicon nitride film (SiN) 207, an SiO₂ film 208 formed byCVD using TEOS (tetraethylorthosilicate) as a source material, ananti-reflection film (BARC) 209, and a patterned resist mask 210 madeof, e.g., ArF are disposed. In this sectional structure, as shown inFIG. 33B, the SiO₂ film 208 is etched relative to the underlying siliconnitride film 207. Also in this case, the same effects described abovecan be obtained by applying a DC voltage to the upper electrode 34.

Further, in the examples described above, the SiOC family film 202 is anetching target (in the main etching or in the main etching and overetching), and the DC voltage application is utilized for the effect ofimproving the selectivity relative to the underlying layer. Accordingly,the DC voltage application may be used solely in the over etching of a2-step process, such that the main etching is performed under normalconditions until a recess being formed reaches a position near theunderlying layer, and then it is switched to the over etching.

Next, an explanation will be given of an embodiment 2 of the presentinvention.

FIG. 34 is a sectional view schematically showing a plasma etchingapparatus according to an embodiment 2 of the present invention. In FIG.34, the constituent elements the same as those shown in FIG. 1 aredenoted by the same reference symbols, and a repetitive descriptionthereon will be omitted.

In place of the upper electrode 34 of the embodiment 1, this embodimentincludes an upper electrode 34′ having the following structure.Specifically, the upper electrode 34′ comprises an outer upper electrode34 a and an inner upper electrode 34 b. The outer upper electrode 34 ahas a ring shape or doughnut shape and is disposed to face a susceptor16 at a predetermined distance. The inner upper electrode 34 b has acircular plate shape and is disposed radially inside the outer upperelectrode 34 a while being insulated therefrom. In terms of plasmageneration, the outer upper electrode 34 a mainly works for it, and theinner upper electrode 34 b assists it.

FIG. 35 is an enlarged partial side view showing a main part of theplasma etching apparatus. As shown in FIG. 35, the outer upper electrode34 a is separated from the inner upper electrode 34 b by an annular gap(slit) of, e.g., 0.25 to 2.0 mm, in which a dielectric body 72 made of,e.g., quartz is disposed. A ceramic body 73 is further disposed in thisgap, but this may be omitted. The two electrodes 34 a and 34 b with thedielectric body 72 sandwiched therebetween form a capacitor. Thecapacitance C₇₂ of this capacitor is set or adjusted to be apredetermined value, on the basis of the size of the gap and thedielectric constant of the dielectric body 72. An insulating shieldmember 42 made of, e.g., alumina (Al₂O₃) and having a ring shape isairtightly interposed between the outer upper electrode 34 a and thesidewall of a chamber 10.

The outer upper electrode 34 a includes an electrode plate 36 a, and anelectrode support 38 a detachably supporting the electrode plate 36 a.The electrode support 38 a is made of a conductive material, such asaluminum with an anodization-processed surface. The electrode plate 36 ais preferably made of a conductor or semiconductor, such as silicon orSiC, having a low resistivity to generate a small Joule heat. The outerupper electrode 34 a is electrically connected to a first RF powersupply 48 the same as that of the embodiment 1 through a matching unit46, an upper feed rod 74, a connector 98, and a feed cylinder 100, thesame as those of the embodiment 1. The output terminal of the matchingunit 46 is connected to the top of the upper feed rod 74.

The feed cylinder 100 has a cylindrical or conical shape, or a shapesimilar to it, and is formed of a conductive plate, such as an aluminumplate or copper plate. The bottom end of the feed cylinder 100 isconnected to the outer upper electrode 34 a continuously in an annulardirection. The top of the feed cylinder 100 is electrically connected tothe bottom of the upper feed rod 74 through the connector 98. Outsidethe feed cylinder 100, the sidewall of the chamber 10 extends upwardabove the height level of the upper electrode 34′ and forms acylindrical grounded conductive body 10 a. The top of the cylindricalgrounded conductive body 10 a is electrically insulated from the upperfeed rod 74 by a tube-like insulating member 74 a. According to thisdesign, the load circuit extending from the connector 98 comprises acoaxial path formed of the feed cylinder 100 and outer upper electrode34 a and the cylindrical grounded conductive body 10 a, wherein the feedcylinder 100 and outer upper electrode 34 a function as a waveguide.

As shown in FIG. 34, the inner upper electrode 34 b includes anelectrode plate 36 b having a number of gas delivery holes 37 b, and anelectrode support 38 b detachably supporting the electrode plate 36 b.The electrode support 38 b is made of a conductor material, such asaluminum with an anodization-processed surface. The electrode support 38b has two gas diffusion cells, i.e., a central gas diffusion cell 40 aand a peripheral gas diffusion cell 40 b, formed therein and separatedby an annular partition member 43, such as an O-ring. The central gasdiffusion cell 40 a and peripheral gas diffusion cell 40 b are connectedto the gas delivery holes 37 b through a number of gas flow channels 41b extending downward. The central gas diffusion cell 40 a, some of anumber of gas flow channels 41 b disposed therebelow, and some of anumber of gas delivery holes 37 b connected thereto constitute a centralshowerhead. The peripheral gas diffusion cell 40 b, some of a number ofgas flow channels 41 b disposed therebelow, and some of a number of gasdelivery holes 37 b connected thereto constitute a peripheralshowerhead.

The gas diffusion cells 40 a and 40 b are supplied with a process gasfrom a common process gas supply source 66 at a predetermined flow-rateratio. More specifically, a gas supply line 64 is extended from theprocess gas supply source 66 and divided into two branch lines 64 a and64 b connected to the gas diffusion cells 40 a and 40 b. The branchlines 64 a and 64 b are connected to gas feed ports 62 a and 62 b formedin the electrode support 38 b, so that the process gas is suppliedthrough the gas feed ports 62 a and 62 b into the gas supply cells 40 aand 40 b. The branch lines 64 a and 64 b are provided with flow ratecontrol valves 71 a and 71 b disposed thereon, respectively. Theconductance values of the flow passages from the process gas supplysource 66 to the gas diffusion cells 40 a and 40 b are equal to eachother. Accordingly, the flow-rate ratio of the process gas supplied intothe central gas supply cell 40 a and peripheral gas supply cell 40 b isarbitrarily adjusted by adjusting the flow rate control valves 71 a and71 b. The gas supply line 64 is provided with a mass-flow controller(MFC) 68 and a switching valve 70 disposed thereon, as in theembodiment 1. The flow-rate ratio of the process gas supplied into thecentral gas diffusion cell 40 a and peripheral gas diffusion cell 40 bis thus adjusted. As a consequence, the ratio (FC/FE) between the gasflow rate FC from the central showerhead and the gas flow rate FE fromthe peripheral showerhead is arbitrarily adjusted. The flow rates perunit area may be set different, for the process gas delivered from thecentral showerhead and peripheral showerhead. Further, gas types or gasmixture ratios may be independently or respectively selected, for theprocess gas delivered from the central showerhead and peripheralshowerhead.

The electrode support 38 b of the inner upper electrode 34 b iselectrically connected to the first RF power supply 48 the same as thatof the embodiment 1 through the matching unit 46, upper feed rod 74,connector 98, and lower feed rod 76, as in the embodiment 1. The lowerfeed rod 76 is provided with a variable capacitor 78 disposed thereon,for variably adjusting capacitance. The variable capacitor 78 can adjustthe balance between the outer electric field intensity and innerelectric field intensity, as described later.

The upper electrode 34′ is also connected to a variable DC power supply50, as in the embodiment 1. Specifically, the variable DC power supply50 is connected to the outer upper electrode 34 a and inner upperelectrode 34 b through a filter 58. The polarity, voltage, and currentof the variable DC power supply 50, and the on/off of an on/off switch52 are controlled by a controller 51, as in the embodiment 1. Althoughthe embodiment 1 includes a filter built in the matching unit 46, thisembodiment includes the filter 58 independently of the matching unit 46.

When an etching process is performed in the plasma etching apparatushaving this structure, an etching target or semiconductor wafer W istransferred into the chamber 10 and placed on the susceptor 16, as inthe embodiment 1. Then, a process gas for etching is supplied from theprocess gas supply source 66 into the central gas diffusion cell 40 aand peripheral gas diffusion cell 40 b at predetermined flow rates andflow-rate ratio to deliver the gas into the chamber 10 through the gasdelivery holes 37 b. At the same time, the exhaust unit 84 is used toexhaust the chamber 10 to maintain the pressure therein at a set value,as in the embodiment 1.

While the etching gas is supplied into the chamber 10, an RF power forplasma generation (60 MHz) is applied from the first RF power supply 48to the upper electrode 34′ at a predetermined power level, and an RF forion attraction (2 MHz) is applied from the second RF power supply 90 tothe lower electrode or susceptor 16 at a predetermined power level.Further, a predetermined voltage is applied from the variable DC powersupply 50 to the outer upper electrode 34 a and inner upper electrode 34b. Furthermore, a DC voltage is applied from the DC power supply 22 tothe electrode 20 of the electrostatic chuck 18 to fix the semiconductorwafer W on the susceptor 16.

The etching gas delivered from the gas delivery holes 37 b of the innerupper electrode 34 b is turned into plasma by glow discharge between theupper electrode 34′ and lower electrode or susceptor 16. Radicals andions generated in this plasma are used to etch the target surface of thesemiconductor wafer W.

In this plasma etching apparatus, the upper electrode 34′ is suppliedwith an RF power within a range covering higher frequencies (form 5 to10 MHz or more at which ions cannot follow). As a consequence, theplasma density is increased with a preferable dissociation state, sothat high density plasma is generated even under a low pressurecondition, as in the embodiment 1.

In the upper electrode 34′, the inner upper electrode 34 b is also usedas a showerhead directly across the semiconductor wafer W, such that theflow-rate ratio of the gas delivered from the central showerhead andperipheral showerhead can be arbitrarily adjusted. As a consequence, thespatial distribution of gas molecular or radical density can becontrolled in the radial direction, so as to arbitrarily control thespatial distribution of an etching characteristic on the basis ofradicals.

Further, as described later, the upper electrode 34′ is operated as anRF electrode for plasma generation, such that the outer upper electrode34 a mainly works for it, and the inner upper electrode 34 b assists it.The ratio of electric field intensity applied to electrons directlybelow the RF electrodes 34 a and 34 b can be adjusted by theseelectrodes. As a consequence, the spatial distribution of plasma densitycan be controlled in the radial direction, so as to arbitrarily andfinely control the spatial property of a reactive ion etchingcharacteristic.

The control over the spatial distribution of plasma density hassubstantially no influence on the control over the spatial distributionof radical density. The control over the spatial distribution of plasmadensity is performed by varying the ratio of electric field intensity orinput power between the outer upper electrode 34 a and inner upperelectrode 34 b. On the other hand, the control over the spatialdistribution of radical density is performed by varying the ratio ofprocess gas flow rate, gas density, or gas mixture between the centralshowerhead and peripheral showerhead. The process gas delivered from thecentral showerhead and peripheral showerhead is dissociated in an areadirectly below the inner upper electrode 34 b. Accordingly, even if thebalance of electric field intensity between the inner upper electrode 34b and outer upper electrode 34 a is changed, it does not have a largeinfluence on the balance of radical generation amount or density betweenthe central showerhead and peripheral showerhead, because bothshowerheads belong to the inner upper electrode 34 b (within the samearea). Thus, the spatial distribution of plasma density and the spatialdistribution of radical density can be controlled substantiallyindependently of each other.

Further, the plasma etching apparatus according to this embodiment isarranged such that most or the majority of plasma is generated directlybelow the outer upper electrode 34 a, which mainly works for plasmageneration, and then diffuses to the position directly below the innerupper electrode 34 b. Accordingly, the showerhead or inner upperelectrode 34 b is less attacked by ions from the plasma. Thiseffectively prevents the gas delivery holes 37 b of the electrode plate36 b from being progressively sputtered, thereby remarkably prolongingthe service life of the electrode plate 36 b, which is a replacementpart. On the other hand, the outer upper electrode 34 a for generatingmost or the majority of plasma has no gas delivery holes at whichelectric field concentration occurs. As a consequence, the outer upperelectrode 34 a is less attacked by ions, and thus there arises no such aproblem in that the outer upper electrode 34 a shortens the servicelife.

Next, with reference to FIGS. 35 and 36, a more detailed explanationwill be given of the control over the spatial distribution of plasmadensity, which is performed by varying the ratio of electric fieldintensity or input power between the outer upper electrode 34 a andinner upper electrode 34 b.

As described above, FIG. 35 shows a main portion of the plasma etchingapparatus according to this embodiment (particularly, a main portion ofplasma generating means). FIG. 36 shows an equivalent circuit of a mainportion of plasma generating means. The structure of the showerheads isnot shown in FIG. 35, while the resistance of respective portions is notshown in FIG. 36.

As described above, the load circuit extending from the connector 98comprises a coaxial path formed of the outer upper electrode 34 a andfeed cylinder 100 and the cylindrical grounded conductive body 10 a,wherein the outer upper electrode 34 a and feed cylinder 100 function asa waveguide J₀. Where the radius (outer radius) of the feed cylinder 100is a₀, and the radius of the cylindrical grounded conductive body 10 ais b, the characteristic impedance or inductance L₀ of this coaxial pathis approximated by the following formula (1).L ₀ =K×In(b/a ₀)  (1)

In this formula, K is a constant determined by the mobility anddielectric constant of a waveguide.

On the other hand, the load circuit extending from the connector 98 alsocomprises a coaxial path formed of the lower feed rod 76 and thecylindrical grounded conductive body 10 a, wherein the former member(76) functions as a waveguide J_(i). Although the inner upper electrode34 b is present on the extension of the lower feed rod 76, the impedanceof lower feed rod 76 is dominant, because the difference in diametersbetween them is very large. Where the radius (outer radius) of the lowerfeed rod 76 is a_(i), the characteristic impedance or inductance L_(i)of this coaxial path is approximated by the following formula (2).L _(i) =K×In(b/a _(i))  (2)

As can be understood from the above formulas (1) and (2), the innerwaveguide J_(i) for transmitting RF to the inner upper electrode 34 bprovides an inductance L_(i) in the same manner as a conventionallyordinary RF system. On the other hand, the outer waveguide J₀ fortransmitting RF to the outer upper electrode 34 a provides a very smallinductance L₀ because of a very large radius. As a consequence, in theload circuit extending from the connector 98 toward the side opposite tothe matching unit 46, RF is transmitted more easily through the outerwaveguide J₀ having a lower impedance (a smaller voltage drop). Theouter upper electrode 34 a is thereby supplied with a larger RF powerP₀, so the electric field intensity E₀ obtained at the bottom surface(plasma contact surface) of the outer upper electrode 34 a becomeshigher. On the other hand, RF is transmitted less easily through theinner waveguide J_(i) having a higher impedance (a larger voltage drop).The inner upper electrode 34 b is thus supplied with an RF power P_(i)smaller than the RF power P₀ supplied to the outer upper electrode 34 a,so the electric field intensity E_(i) obtained at the bottom surface(plasma contact surface) of the inner upper electrode 34 b becomes lowerthan the electric field intensity E₀ on the outer upper electrode 34 aside.

As described above, according to this upper electrode 34′, electrons areaccelerated by a stronger electric field E₀ directly below the outerupper electrode 34 a, while electrons are accelerated by a weakerelectric field E₀ directly below the inner upper electrode 34 b. In thiscase, most or the majority of plasma P is generated directly below theouter upper electrode 34 a, while a subsidiary part of the plasma P isgenerated directly below the inner upper electrode 34 b. Then, the highdensity plasma generated directly below the outer upper electrode 34 adiffuses radially inward and outward, so the plasma density becomes moreuniform in the radial direction within the plasma process space betweenthe upper electrode 34′ and susceptor 16.

In the coaxial path formed of the outer upper electrode 34 a and feedcylinder 100 and the cylindrical grounded conductive body 10 a, themaximum transmission power P_(max) depends on the radius a₀ of the feedcylinder 100 and the radius b of the cylindrical grounded conductivebody 10 a, and is given by the following formula (3).Pmax/E ₀ ² max=a ₀ ² [In(b/a ₀)]²/2Z ₀  (3)

In the above formula, Z₀ is the input impedance of this coaxial pathviewing from the matching unit 46, and E_(0max) is the maximum electricfield intensity of the RF transmission system.

In the formula (3), the maximum transmission power P_(max) takes on themaximum value when (b/a₀)≈1.65. Accordingly, in order to improve thepower transmission efficiency of the outer waveguide J₀, the ratio(b/a₀) of the radius of the cylindrical grounded conductive body 10 arelative to the radius of the feed cylinder 100 is most preferably setat about 1.65. This ratio is preferably set to be at least within arange of 1.2 to 2.0, and more preferably within a range of 1.5 to 1.7.

In order to arbitrarily and finely control the spatial distribution ofplasma density, it is preferable to adjust the ratio or balance betweenthe outer electric field intensity E₀ directly below the outer upperelectrode 34 a (or the input power P₀ into the outer upper electrode 34a side) and the inner electric field intensity E_(i) directly below theinner upper electrode 34 b (or the input power P_(i) into the innerupper electrode 34 b side). The lower feed rod 76 is provided with thevariable capacitor 78 disposed thereon as means for adjusting the ratioor balance. FIG. 37 shows the relationship between the capacitance C₇₈of this variable capacitor 78 and the ratio of the input power P_(i)into the inner upper electrode 34 b relative to the total input power.As shown in FIG. 37, the capacitance C₇₈ of the variable capacitor 78 isadjusted to increase or decrease the impedance or reactance of the innerwaveguide J_(i), thereby changing the relative ratio between the voltagedrop through the outer waveguide J₀ and the voltage drop through theinner waveguide J_(i). As a consequence, it is possible to adjust theratio between the outer electric field intensity E₀ (outer input powerP₀) and the inner electric field intensity E_(i) (inner input powerP_(i)).

In general, the ion sheath impedance that causes an electric potentialdrop of plasma is capacitive. In the equivalent circuit shown in FIG.36, it is assumed that the sheath impedance capacitance directly belowthe outer upper electrode 34 a is C_(po), and the sheath impedancecapacitance directly below the inner upper electrode 34 b is C_(pi).Further, the capacitance C₇₂ of the capacitor formed between the outerupper electrode 34 a and inner upper electrode 34 b cooperates with thecapacitance C₇₈ of the variable capacitor 78 in changing the balancebetween the outer electric field intensity E₀ (outer input power P₀) andinner electric field intensity E_(i) (inner input power P_(i)). Thecapacitance C₇₂ is preferably set or adjusted to optimize the variablecapacitor's 78 function of adjusting the balance of electric fieldintensity (input power).

On the other hand, as in the embodiment 1, a DC voltage is applied fromthe variable DC power supply 50 through the filter 58 to the outer upperelectrode 34 a and inner upper electrode 34 b. As a consequence, thespatial distribution of plasma density is controlled, as describedabove. At the same time, it is possible to exercise the same effects asthose in the embodiment 1, i.e., the sputtering function due to a deeperV_(dc), the plasma pressing function due to a larger plasma sheathlength, the electron supply function onto the wafer W, the plasmapotential adjustment function, and the plasma density increase function.

As described above, the effects obtained by the upper electrode 34′formed of two parts, i.e., the outer upper electrode 34 a and innerupper electrode 34 b, are combined with the effects obtained byapplication of a predetermined DC voltage to the upper electrode 34′, sothe plasma control can be more preferably realized.

In the example shown in FIG. 34, a DC voltage is applied to both of theouter upper electrode 34 a and inner upper electrode 34 b.Alternatively, a DC voltage may be applied to either one of them.

In the example shown in FIG. 34, a DC voltage is applied from onevariable DC power supply 50 to both of the outer upper electrode 34 aand inner upper electrode 34 b. Alternatively, as shown in FIG. 38, twovariable DC power supplies 50 a and 50 b may be used to apply DCvoltages to the outer upper electrode 34 a and inner upper electrode 34b, respectively, through switches 52 a and 52 b, and filters 58 a and 58b. In this case, the DC voltages applied to the outer upper electrode 34a and inner upper electrode 34 b can be independently controlled,thereby performing the plasma control in a better manner.

Further, as shown in FIG. 39, a variable DC power supply 50′ may beinterposed between the outer upper electrode 34 a and inner upperelectrode 34 b. In this case, one of the terminals is connected to theouter upper electrode 34 a and the other terminal is connected to theinner upper electrode 34 b. As a consequence, in addition to the effectsdescribed above, the plasma density ratio between the inner upperelectrode 34 b and outer upper electrode 34 a can be more finelyadjusted to improve the etching characteristic control planarly on thewafer. In FIG. 39, a reference symbol 52′ denotes an on/off switch, andreference symbols 58 a′ and 58 b′ denote filters.

Where the plasma etching apparatus according to the embodiment 2 is usedto etch an insulating film (for example, Low-k film) disposed on a waferW, the following combination of gases is particularly preferably used asa process gas.

Specifically, where over etching is performed under via-etchingconditions, a combination of C₅F₈, Ar, and N₂ may be preferably used asa process gas. In this case, the selectivity of an insulating filmrelative to an underlying film (SiC, SiN, etc.) can become larger.

Alternatively, where trench etching conditions are used, CF₄ or acombination of (C₄F₈, CF₄, Ar, N₂, and O₂) may be preferably used as aprocess gas. In this case, the selectivity of an insulating filmrelative to a mask can become larger.

Alternatively, where HARC etching conditions are used, a combination of(C₄F₆, CF₄, Ar, and O₂), (C₄F₆, C₃F₈, Ar, and O₂), or (C₄F₆, CH₂F₂, Ar,and O₂) may be preferably used as a process gas. In this case, theetching rate of an insulating film can become higher.

The process gas is not limited to the examples described above, andanother combination of (CxHyFz gas/an additive gas such as N₂ or O₂/adilution gas) may be used.

In the embodiment 1 and embodiment 2, the first RF power and second RFpower may have frequencies, as follows. Specifically, the frequency ofthe first RF power may be one of 13.56 MHz, 27 MHz, 40 MHz, 60 MHz, 80MHz, 100 MHz, and 160 MHz, while the frequency of the second RF powermay be one of 380 kHz, 800 kHz, 1 MHz, 2 MHz, 3.2 MHz, and 13.56 MHz.They are suitably combined in accordance with a process to be performed.

The embodiments described above are exemplified by plasma etchingapparatuses, but they may be applied to other apparatuses that utilizeplasma to process a semiconductor substrate, such as a plasma filmformation apparatus.

Additional advantages and modifications will readily occur to thoseskilled in the art. Therefore, the invention in its broader aspects isnot limited to the specific details and representative embodiments shownand described herein. Accordingly, various modifications may be madewithout departing from the spirit or scope of the general inventiveconcept as defined by the appended claims and their equivalents.

What is claimed is:
 1. A plasma processing apparatus comprising: aprocess container that forms a process space to accommodate a targetsubstrate; an exhaust unit connected to an exhaust port of the processcontainer to vacuum-exhaust gas from inside the process container; anexhaust plate interposed between the process space and the exhaust portto rectify a flow of exhaust gas; a first electrode and a secondelectrode disposed opposite each other within the process container, thefirst electrode being an upper electrode and the second electrode beinga lower electrode and configured to support the target substrate througha mount face; a conductive focus ring disposed on the second electrodeto surround the target substrate; an electrode support made of aninsulating material and including a first portion interposed between thesecond electrode and a bottom of the process container and a secondportion surrounding the second electrode; a first RF power applicationunit configured to apply a first RF power to the first electrode; asecond RF power application unit configured to apply a second RF powerto the second electrode, the second RF power having a frequency lowerthan that of the first RF power; a DC power supply configured to apply aDC voltage to the first electrode; a process gas supply unit configuredto supply a process gas into the process container; a first shield partcovering a side surface of the electrode support and formed of a firstconductive internal body and a first insulator covering the firstconductive internal body; and a conductive member disposed within theprocess container and grounded to release through plasma a currentcaused by the DC voltage applied from the DC power supply to the firstelectrode, the conductive member being supported by the first shieldpart and laterally protruding therefrom at a position that is located,in a height-wise direction, between the mount face and the exhaust plateso as for the conductive member to be exposed to the plasma, and theconductive member being grounded through the first conductive internalbody of the first shield part.
 2. The plasma processing apparatusaccording to claim 1, wherein the DC power supply is configured suchthat any one of application voltage, application current, andapplication power to the first electrode is variable.
 3. The plasmaprocessing apparatus according to claim 1, further comprising a controlunit configured to control any one of application voltage, applicationcurrent, and application power from the DC power supply to the firstelectrode.
 4. The plasma processing apparatus according to claim 3,wherein the control unit is configured to control whether the DC voltageis to be applied or not, from the DC power supply to the firstelectrode.
 5. The plasma processing apparatus according to claim 3,further comprising a detector configured to detect a generated plasmastate, wherein the control unit controls any one of application voltage,application current, and application power from the DC power supply tothe first electrode, based on information from the detector.
 6. Theplasma processing apparatus according to claim 1, wherein anelectrostatic chuck configured to hold the target substrate by anelectrostatic attraction force is disposed on the second electrode, andthe mount face is defined by the electrostatic chuck.
 7. The plasmaprocessing apparatus according to claim 1, wherein the first RF powerapplied to the first electrode has a frequency of 13.56 MHz or more. 8.The plasma processing apparatus according to claim 7, wherein the firstRF power applied to the first electrode has a frequency of 40 MHz ormore.
 9. The plasma processing apparatus according to claim 1, whereinthe second RF power applied to the second electrode has a frequency of13.56 MHz or less.
 10. The plasma processing apparatus according toclaim 1, wherein the DC power supply is configured to apply a voltagewithin a range of −2,000 to +1,000V.
 11. The plasma processing apparatusaccording to claim 1, wherein the DC voltage applied from the DC powersupply has an absolute value of 500V or more.
 12. The plasma processingapparatus according to claim 1, wherein the DC voltage is a negativevoltage having an absolute value larger than that of a self-bias voltagegenerated on a surface of the first electrode by the first RF powerapplied to the first electrode.
 13. The plasma processing apparatusaccording to claim 1, wherein a surface of the first electrode facingthe second electrode is made of a silicon-containing substance.
 14. Theplasma processing apparatus according to claim 1, wherein a cover plateis disposed to partly cover the conductive member, and the cover plateis moved relative to the conductive member by a driving mechanism tochange a portion of the conductive member to be exposed to plasma. 15.The plasma processing apparatus according to claim 1, wherein theconductive member is columnar and partly exposed to plasma, and theconductive member is rotated about a center thereof by driving mechanismto change a portion of the conductive member to be exposed to plasma.16. The plasma processing apparatus according to claim 1, wherein acover film having a stepped shape and made of a material to be etched byplasma is disposed to partly cover the conductive member, and the coverfilm is configured to be etched to change a portion of the conductivemember to be exposed to plasma.
 17. The plasma processing apparatusaccording to claim 1, wherein the apparatus further comprises a secondshield part covering an inner sidewall of the process container andincluding a second insulator covering a surface of the second shieldpart.
 18. The plasma processing apparatus according to claim 17, whereinthe second shield part is formed of a second conductive internal bodyand the second insulator covering the second conductive internal body.19. The plasma processing apparatus according to claim 18, wherein thefirst and second conductive internal bodies are made of aluminum and thefirst and second insulators are made of ceramic.
 20. The plasmaprocessing apparatus according to claim 1, wherein the first RF power isa power for plasma generation and the second RF power is a power for ionattraction.
 21. The plasma processing apparatus according to claim 1,wherein the process gas supply unit is configured to supply, as theprocess gas, an etching gas for etching the target substrate.
 22. Theplasma processing apparatus according to claim 1, wherein a plasmageneration area is defined between the first and second electrodes inthe height-wise direction, and the conductive member is located outsideof the plasma generation area in the height-wise direction.